Balsa wood (Ochroma pyramidale)

spore: profile
id: balsa-wood
spore_version: 0.2
family: wood
name: Balsa wood (Ochroma pyramidale)
role: Low-density natural wood for light cores in composites, model structures and light-aircraft panels
category: living
type: bio-grown-building-materials
summary: |
  Balsa wood is the wood of the tree Ochroma pyramidale. Its dry wood density runs from 40 to 475 kg/m3 across the range quoted by Wikipedia, with about 160 kg/m3 typical. The High grade (200 to 400 kg/m3) listed by Spot Material has a tensile modulus of 5.5 to 6 GPa, a tensile strength of 16.3 to 40 MPa and a thermal conductivity of 0.9 to 1.2 W/mK. Its green moisture content is 200 to 400 per cent, so it is kiln dried before use (WoodSolutions).
best_for: Light cores in composites and model structures, where low density matters more than strength
weakest_at: Low toughness (up to 15 Nm as printed by WoodSolutions) and very high green moisture content that must be dried out
identity:
  formula: 'Wood of Ochroma pyramidale: cell walls of cellulose, hemicellulose and lignin, with air-filled cells'
  source: wikipedia-balsa
  where: 'Taxonomy section: Ochroma pyramidale (Cav. ex Lam.) Urb.; sole member of genus Ochroma; family Malvaceae (Wikipedia, Balsa)'
tags:
  applications:
    - structures
properties:
  - benchmark: density
    label: Dry wood density, range
    value: 40
    value_high: 475
    bound: range
    unit: kg/m3
    scope: material
    conditions:
      basis: dry wood density range as printed, Ochroma pyramidale
      moisture: not stated on the page
    method: Range printed in the Wikipedia article (the article cites Porter 2004, WoodSolutions and Borrega et al. 2015 for it)
    status: ground
    source: wikipedia-balsa
    where: Wood density paragraph, density range (2.5 to 29.7 lb/cu ft also printed)
  - benchmark: density
    label: Dry wood density, typical
    value: 160
    unit: kg/m3
    scope: material
    conditions:
      basis: typical dry wood density, printed as around 160 kg/m3
      moisture: not stated on the page
    method: Typical value printed in the Wikipedia article (same refs as the range)
    status: ground
    source: wikipedia-balsa
    where: Wood density paragraph, typical value (10 lb/cu ft also printed)
  - benchmark: density
    label: Commercial range, printed with the 160 value
    value: 120
    value_high: 220
    bound: range
    unit: kg/m3
    scope: material
    conditions:
      basis: density printed as 160 (120-220); the page gives the commercially preferred range as 120-160
      moisture: moisture basis not stated on the page
    method: Printed on the WoodSolutions balsa page; the page prints the unit as kgm3, written here as kg/m3
    status: ground
    source: woodsolutions-balsa
    where: Density row of the species property table
  - benchmark: density
    label: Density per standard, seasoned
    value: 160
    unit: kg/m3
    scope: material
    conditions:
      basis: density per standard, seasoned wood
      moisture: moisture basis not stated; page lists the unseasoned value separately as 700 kg/m3
    method: Printed on the WoodSolutions balsa page under Density per Standard; unit printed as kgm3, written as kg/m3
    status: ground
    source: woodsolutions-balsa
    where: Density per Standard row
  - benchmark: density
    label: High grade density
    value: 200
    value_high: 400
    bound: range
    unit: kg/m3
    scope: material
    conditions:
      grade: High (200-400 kg/m3), as listed by Spot Material
      test: not stated on the page
    method: Range printed on the Spot Material High grade page
    status: ground
    source: spotmaterial-balsa-high
    where: Density row of the design properties table
  - benchmark: specific_gravity
    label: Specific gravity, light density class
    value: 0.1
    unit: '-'
    scope: material
    conditions:
      density_class: light
      basis: density class as labelled on the page; unit not printed (dimensionless)
    method: Printed in the grade table of the 1958 Forest Products Journal article; no moisture or test basis given
    status: ground
    source: forestprod-balsa-1958
    where: Grade table, Light row
  - benchmark: elastic_modulus
    label: Tensile modulus, High grade
    value: 5.5
    value_high: 6
    bound: range
    unit: GPa
    scope: material
    conditions:
      grade: High (200-400 kg/m3), as listed by Spot Material
      test: tensile, as printed; test standard not stated
    method: Range printed on the Spot Material High grade page; the page gives no separate data source
    status: ground
    source: spotmaterial-balsa-high
    where: Design properties table, Tensile modulus row
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, High grade
    value: 16.3
    value_high: 40
    bound: range
    unit: MPa
    scope: material
    conditions:
      grade: High (200-400 kg/m3), as listed by Spot Material
      test: tensile, as printed; test standard not stated
    method: Range printed on the Spot Material High grade page
    status: ground
    source: spotmaterial-balsa-high
    where: Design properties table, Tensile strength row
  - benchmark: flexural_modulus
    label: Flexural modulus, High grade
    value: 5
    unit: GPa
    scope: material
    conditions:
      grade: High (200-400 kg/m3), as listed by Spot Material
      test: not stated on the page
    method: Single value printed on the Spot Material High grade page
    status: ground
    source: spotmaterial-balsa-high
    where: Design properties table, Flexural modulus row
  - benchmark: flexural_strength
    label: Modulus of rupture, High grade
    value: 28
    value_high: 70
    bound: range
    unit: MPa
    scope: material
    conditions:
      grade: High (200-400 kg/m3), as listed by Spot Material
      test: not stated on the page
    method: Range printed on the Spot Material High grade page. The same page prints a flexural strength of 350 MPa, which is left out (see gaps)
    status: ground
    source: spotmaterial-balsa-high
    where: Design properties table, Modulus of rupture row
  - benchmark: shear_modulus
    label: Shear modulus, High grade
    value: 0.28
    value_high: 0.5
    bound: range
    unit: GPa
    scope: material
    conditions:
      grade: High (200-400 kg/m3), as listed by Spot Material
      test: not stated on the page
    method: Range printed on the Spot Material High grade page
    status: ground
    source: spotmaterial-balsa-high
    where: Design properties table, Shear modulus row
  - benchmark: compressive_strength
    label: Compressive strength, High grade
    value: 20
    value_high: 40
    bound: range
    unit: MPa
    scope: material
    conditions:
      grade: High (200-400 kg/m3), as listed by Spot Material
      direction: not stated on the page
    method: Range printed on the Spot Material High grade page; compressive_strength is not in the canonical property file (see gaps)
    status: ground
    source: spotmaterial-balsa-high
    where: Design properties table, Compressive strength row
  - benchmark: thermal_conductivity
    label: Thermal conductivity, High grade
    value: 0.9
    value_high: 1.2
    bound: range
    unit: W/mK
    scope: material
    conditions:
      grade: High (200-400 kg/m3), as listed by Spot Material
      temperature: not stated on the page
    method: Range printed on the Spot Material High grade page
    status: ground
    source: spotmaterial-balsa-high
    where: Design properties table, Thermal conductivity row
  - benchmark: janka_hardness
    label: Janka hardness, High grade
    value: 0.4
    value_high: 0.7
    bound: range
    unit: kN
    scope: material
    conditions:
      grade: High (200-400 kg/m3), as listed by Spot Material
      test: not stated on the page
    method: Range printed on the Spot Material High grade page; janka_hardness is not in the canonical property file (see gaps)
    status: ground
    source: spotmaterial-balsa-high
    where: Design properties table, Janka hardness row
  - benchmark: janka_hardness
    label: Janka hardness, as quoted from USDA
    value: 22
    value_high: 167
    bound: range
    unit: lbf
    scope: material
    conditions:
      basis: Janka hardness range as printed (98 to 743 N also printed); the article cites Wiepking and Doyle 1955 (USDA Forest Service)
      moisture: not stated
    method: Range printed in the Wikipedia article, citing Wiepking and Doyle 1955
    status: ground
    source: wikipedia-balsa
    where: Physical properties paragraph, Janka hardness (ref. 11)
  - benchmark: shrinkage_tangential
    label: Tangential shrinkage
    value: 4.9
    unit: '%'
    scope: material
    conditions:
      basis: shrinkage as printed; the page does not say whether it is from green or dry to a given moisture
      rating: page's shrinkage rating is unclear
    method: Printed on the WoodSolutions balsa page; shrinkage_tangential is not in the canonical property file (see gaps)
    status: ground
    source: woodsolutions-balsa
    where: Shrinkage row, tangential
  - benchmark: shrinkage_radial
    label: Radial shrinkage
    value: 1.8
    unit: '%'
    scope: material
    conditions:
      basis: shrinkage as printed; the page does not say whether it is from green or dry to a given moisture
      rating: page's shrinkage rating is unclear
    method: Printed on the WoodSolutions balsa page; shrinkage_radial is not in the canonical property file (see gaps)
    status: ground
    source: woodsolutions-balsa
    where: Shrinkage row, radial
  - benchmark: moisture_content_green
    label: Green moisture content
    value: 200
    value_high: 400
    bound: range
    unit: '%'
    scope: material
    conditions:
      basis: green (freshly cut) wood; moisture basis not stated, printed as 200-400%
      state: green
    method: Printed on the WoodSolutions balsa page, which calls it very high and relevant to kiln drying; moisture_content_green is not in the canonical property file (see gaps)
    status: ground
    source: woodsolutions-balsa
    where: Green moisture content row
  - benchmark: toughness
    label: Toughness, upper value
    value: 15
    bound: upper
    unit: Nm
    scope: material
    conditions:
      basis: printed as Low, up to 15 Nm for seasoned and unseasoned wood; the page gives no test standard
      state: seasoned and unseasoned
    method: Printed on the WoodSolutions balsa page; toughness is not in the canonical property file (see gaps)
    status: ground
    source: woodsolutions-balsa
    where: Toughness row
corrosion:
  - environment: Above ground, exposed to weather
    headline: WoodSolutions prints above-ground durability ranges of 0-20 yrs (usually under 5), 21-40, 41-64 and more than 60 yrs.
    effect: The page gives these durability ranges as classes. It does not say which exposure or test standard applies, and it does not name the class that holds balsa.
    conditions:
      exposure: above ground, per the WoodSolutions durability row
      basis: durability classes as printed; no test standard stated
    source: woodsolutions-balsa
    where: Above-ground durability row
    rating: unknown
  - environment: In ground, in contact with soil
    headline: WoodSolutions prints in-ground durability ranges of 0-7, 7-15, 15-40 and more than 40 yrs.
    effect: The page shows these as classes. It does not state the test standard or which class balsa belongs to.
    conditions:
      exposure: in ground, per the WoodSolutions durability row
      basis: durability classes as printed; no test standard stated
    source: woodsolutions-balsa
    where: In-ground durability row
    rating: unknown
  - environment: Green wood, freshly cut, before drying
    headline: Green balsa holds 200-400% moisture, which the WoodSolutions page calls very high and relevant to kiln drying.
    effect: Wood that holds this much water shrinks as it dries. The page prints tangential shrinkage of 4.90% and radial shrinkage of 1.80%, but it does not give the moisture range over which these apply.
    conditions:
      state: green
      basis: moisture basis not stated on the page
    source: woodsolutions-balsa
    where: Green moisture content row; Shrinkage rows
    rating: unknown
  - environment: Wood in general, moisture in the cell walls
    headline: Wood retains 8-16% of the water in its cell walls, which softens it.
    effect: The Wikipedia article on wood says water in the cell walls makes wood softer and more pliable. This is general wood, not measured on balsa.
    conditions:
      basis: general wood, not balsa-specific
      moisture: 8-16% of the water in the cell walls, as printed
    source: wikipedia-wood
    where: Water content section
    rating: unknown
  - environment: Biological decay by rot-producing fungi
    headline: Rot-producing fungi make wood weaker and leave colours that show the weakness.
    effect: The Wikipedia article on wood says certain rot-producing fungi impart colours that are symptomatic of weakness. No decay rate for balsa is given in any source read in this run.
    conditions:
      basis: general wood, not balsa-specific
    source: wikipedia-wood
    where: Colour section
    rating: unknown
risks:
  hazards:
    - text: OSHA's wood dust overview says wood dust becomes a potential health problem when wood particles from processes such as sanding and cutting become airborne, and that breathing these particles may cause allergic respiratory symptoms, mucosal and non-allergic respiratory symptoms, and cancer. The page also says the extent of these hazards and the associated wood types have not been clearly established, and it gives no numeric exposure limit. No balsa-specific hazard data were found.
      ghs: []
      source: osha-wood-dust
      where: Overview section, wood dust hazards
  failure_risks:
    - mode: Dimensional change as the wood dries from green
      trigger: Drying from a green moisture content of 200-400%
      consequence: Tangential shrinkage of 4.90% and radial shrinkage of 1.80% as printed by WoodSolutions; the page does not give the moisture range for these figures.
      severity: moderate
      source: woodsolutions-balsa
      where: Shrinkage rows; Green moisture content row
    - mode: Low toughness
      trigger: Impact or toughness loading of seasoned or unseasoned balsa
      consequence: WoodSolutions prints toughness as Low, up to 15 Nm for both seasoned and unseasoned wood.
      severity: moderate
      source: woodsolutions-balsa
      where: Toughness row
  side_effects: []
  handling:
    - text: WoodSolutions says the 200-400% green moisture content is very high and relevant to kiln drying, so green balsa must be dried before use.
      source: woodsolutions-balsa
      where: Green moisture content row and text
    - text: WoodSolutions prints tangential shrinkage of 4.90% and radial shrinkage of 1.80%, so dimensions change during drying.
      source: woodsolutions-balsa
      where: Shrinkage rows
  mitigations: []
uses:
  - application: structures
    device: Core panels for composites (wind turbine blades, surfboards, boat decks, table tennis rackets)
    example: Wikipedia says more than 90% of the world's balsa wood volume is prepared into end-grain panels for the composites industry (no citation given in the article).
    source: wikipedia-balsa
    where: Uses section, composite core paragraph
  - application: structures
    device: Lightweight structures and aircraft parts (model bridges, model buildings, model aircraft, full-size light aircraft such as the World War II de Havilland Mosquito)
    example: Wikipedia lists balsa for model bridges, model buildings and model aircraft, and for components of full-size light aircraft, notably the World War II de Havilland Mosquito.
    source: wikipedia-balsa
    where: Common uses list, first and second items
  - application: structures
    device: Core stock for doors, boat hulls, aircraft panels, wall or partition insulation and buoyant marine articles
    example: The 1958 Forest Products Journal article lists balsa core stock for doors, boat hulls, aircraft panels, wall or partition insulation, and buoyant marine articles.
    source: forestprod-balsa-1958
    where: Uses paragraph
supply:
  - subject: Balsa wood, commercial supply
    abundance: 'Wikipedia gives two Ecuador shares for commercial balsa that disagree: 95% or more (Introduction) and 70% or more (Cultivation section). About 60% of balsa is plantation grown in densely packed patches (Cultivation). The article gives no year for these shares, and we found no second source for them.'
    producers: []
    critical_lists: []
    recycling: Not found in any source we hold.
    substitutes: []
    source: wikipedia-balsa
    where: Introduction; Cultivation section
  - subject: Balsa wood, plantation harvest
    abundance: Wikipedia says trees are harvested after six to ten years of growth in Ecuador, and at four to five years of age in Papua New Guinea. Plantations hold about 1000 trees per hectare (400 per acre), against two to three per hectare in nature.
    producers: []
    critical_lists: []
    recycling: Not found in any source we hold.
    substitutes: []
    source: wikipedia-balsa
    where: Cultivation section
  - subject: Balsa wood, export leader
    abundance: Argus Media quotes the Global Development Policy Center of Boston University that Ecuador is the world's largest exporter of balsa wood. The article gives no production share and no plantation share.
    producers: []
    critical_lists: []
    recycling: Not found in any source we hold.
    substitutes: []
    source: argus-ecuador-balsa
    where: Article body, sentence citing the Global Development Policy Center of Boston University
media: []
documents:
  - title: Properties and uses of balsa (Forest Products Journal, 1958, 8(8):27A-30A)
    type: paper
    url: https://forestprod.org/knowledge-base/properties-and-uses-of-balsa
    year: 1958
  - title: Mechanics of balsa (Ochroma pyramidale) wood, Borrega and Gibson, Mechanics of Materials 84 (2015), abstract page
    type: paper
    url: https://dspace.mit.edu/handle/1721.1/108580
    year: 2015
  - title: 'Spot Material: Balsa, High grade (200-400 kg/m3) design properties'
    type: database
    url: https://spotmaterial.com/material/balsa/high-200-400-kg-m3/
  - title: 'OSHA: Wood dust overview page'
    type: report
    url: https://www.osha.gov/wood-dust
  - title: 'Argus Media: Ecuador balsa wood exports for wind turbines decline (article dated 13/07/22 as printed)'
    type: report
    url: https://www.argusmedia.com/en/news/2350426-ecuador-balsa-wood-exports-for-wind-turbines-decline
gaps:
  - 'Borrega and Gibson 2015 full text not read: the PDF download returned an HTML page, not a PDF. No modulus or strength value from the paper is used; only the abstract''s density range (roughly 60 to 380 kg/m3) and its linear-in-density statement are cited.'
  - No balsa-specific chemical composition found. The recipe uses general wood composition from the Wikipedia Wood article (cellulose, hemicellulose, lignin).
  - One hazard entry added from the OSHA wood dust overview (osha-wood-dust). That page is general to wood dust, gives no numeric exposure limit and does not mention skin effects. No balsa-specific hazard data found; the two NIOSH pages tried returned HTTP 404.
  - No standard designation code (UNS, EN, ASTM, DIN, JIS) found for balsa in the pages read. designations left out.
  - No supply share with a year found. The two Ecuador shares in Wikipedia (95% or more and 70% or more) conflict and are both printed. The MDPI paper (HTTP 403) and the EIA PDF (binary, unreadable) could not be read. The Argus article gives no share, only that Ecuador is the largest exporter.
  - No critical-mineral list applies to balsa; USGS and EU lists were not checked for a wood.
  - No ageing or durability test standard found. The durability ranges on WoodSolutions are classes without test conditions.
  - 'Spot Material flexural strength of 350 MPa not used: it lies far outside the same page''s modulus of rupture of 28-70 MPa, and it is treated as a typo.'
  - 'Spot Material Poisson''s ratio of 0.23-0.66 not used: the upper value is above 0.5, the limit for isotropic materials, and the page gives no explanation.'
  - Forest Products Journal light-class modulus of rupture printed as –1,375 psi, with a dash that may be a print artifact. Not used.
  - WoodSolutions MOR, MOE, compression, hardness and stress-grade figures have no unit printed or are grade codes. Not used.
  - Spot Material temperature range of -200 to 150 °C and its cost, embodied energy and carbon footprint are printed without basis or are not canonical properties. Not used.
  - 'Non-canonical property names used (not in spores/property-canon.yaml): specific_gravity, compressive_strength, janka_hardness, shrinkage_tangential, shrinkage_radial, moisture_content_green, toughness.'
  - Test standard, moisture basis and test conditions are not stated for most values. Each property's conditions say so.
  - No images sourced in this run. media left empty.
sources:
  forestprod-balsa-1958:
    title: Properties and uses of balsa (Forest Products Journal, 1958)
    id: Forest Products Journal 8(8):27A-30A, 1958
    url: https://forestprod.org/knowledge-base/properties-and-uses-of-balsa
    year: 1958
    kind: paper
    license: as shown on the knowledge-base page
  spotmaterial-balsa-high:
    title: 'Spot Material: balsa, High grade (200-400 kg/m3) design properties'
    id: Spot Material balsa page, High grade
    url: https://spotmaterial.com/material/balsa/high-200-400-kg-m3/
    kind: database
    license: as shown on the page
    note: 'Printed figures read in this run: density 200-400 kg/m3; tensile modulus 5.5-6 GPa; tensile strength 16.3-40 MPa; flexural modulus 5 GPa; modulus of rupture 28-70 MPa; flexural strength 350 MPa (not used); shear modulus 0.28-0.5 GPa; compressive strength 20-40 MPa; thermal conductivity 0.9-1.2 W/mK; Janka hardness 0.4-0.7 kN. No test conditions printed.'
  wikipedia-balsa:
    title: Balsa (Wikipedia article)
    id: Wikipedia, Balsa
    url: https://en.wikipedia.org/wiki/Balsa
    kind: web
    license: CC BY-SA (Wikipedia)
    note: 'Printed figures read in this run: dry wood density range 40 to 475 kg/m3 (2.5 to 29.7 lb/cu ft); typical around 160 kg/m3 (10 lb/cu ft); Janka hardness 22 to 167 lbf (98 to 743 N); more than 90% of world balsa volume is made into end grain panels for composites; Ecuador supplies 95% or more of commercial balsa (Introduction) and 70% or more (Cultivation section); about 60% plantation grown in densely packed patches; harvested after six to ten years in Ecuador and at 4-5 years of age in Papua New Guinea; plantations about 1000 trees per hectare (400 per acre) against two to three per hectare in nature; lifespan 30 to 40 years; maximum height 30 metres.'
  woodsolutions-balsa:
    title: 'WoodSolutions: Balsa (Ochroma pyramidale) species page'
    id: WoodSolutions, balsa
    url: https://www.woodsolutions.com.au/wood-species/balsa
    kind: web
    license: as shown on the page
    note: 'Printed figures read in this run: density 160 (120-220) kgm3, commercially preferred 120-160 kgm3; density per standard 160 kg/m3 seasoned and 700 kg/m3 unseasoned; green moisture content 200-400%, called very high and relevant to kiln drying; shrinkage tangential 4.90%, radial 1.80%; unit movement tangential 0.27%, radial 0.10%; toughness Low, up to 15 Nm; in-ground durability 0-7, 7-15, 15-40 and more than 40 yrs; above-ground durability 0-20 yrs (usually under 5), 21-40, 41-64 and more than 60 yrs. Modulus of rupture, modulus of elasticity, compression and hardness values are printed without a unit and are not used.'
  mit-borrega-gibson-2015:
    title: Mechanics of balsa (Ochroma pyramidale) wood
    id: doi:10.1016/j.mechmat.2015.01.014 (Mechanics of Materials 84, pp. 75-90)
    url: https://dspace.mit.edu/handle/1721.1/108580
    year: 2015
    kind: paper
    license: MIT DSpace record; full-text PDF not opened
    note: 'Abstract as read on the DSpace record (full-text PDF not read): balsa densities of roughly 60 to 380 kg/m3; in axial compression, bending and torsion, elastic modulus and strength increase linearly with density; radial compression varies nonlinearly. The abstract gives no numeric modulus or strength values.'
  wikipedia-wood:
    title: Wood (Wikipedia article)
    id: Wikipedia, Wood
    url: https://en.wikipedia.org/wiki/Wood
    kind: web
    license: CC BY-SA (Wikipedia)
    note: 'General wood, not balsa-specific: cell walls composed of micro-fibrils of cellulose (40-50%) and hemicellulose (15-25%) impregnated with lignin (15-30%); the wood retains 8-16% of the water in the cell walls; water makes wood softer and more pliable; certain rot-producing fungi impart colours symptomatic of weakness.'
  osha-wood-dust:
    title: 'OSHA: Wood dust overview page'
    id: OSHA wood dust overview
    url: https://www.osha.gov/wood-dust
    kind: web
    license: as shown on the page
    note: 'Printed text read in this run: breathing these particles may cause allergic respiratory symptoms, mucosal and non-allergic respiratory symptoms, and cancer; the extent of these hazards and the associated wood types have not been clearly established. No numeric exposure limit is given; skin effects are not mentioned; exposure limits are addressed in specific OSHA standards for general industry.'
  argus-ecuador-balsa:
    title: 'Argus Media: Ecuador balsa wood exports for wind turbines decline'
    id: Argus Media news article, dated 13/07/22 as printed
    url: https://www.argusmedia.com/en/news/2350426-ecuador-balsa-wood-exports-for-wind-turbines-decline
    kind: web
    license: as shown on the page
    note: 'Printed text read in this run: Ecuador is the world''s largest exporter of balsa wood, according to the Global Development Policy Center of Boston University. The article gives no production share and no plantation share.'
license: CC-BY-4.0
updated: '2026-11-01'
review:
  status: draft
  method: assistant
  checked_values: 19
  unreachable: 2
  caveats: 3
  note: Read by an AI assistant on 2026-11-01 from four pages named in the brief plus WoodSolutions and the Wikipedia Wood article. 26 values as printed. The MIT PDF and two NIOSH pages could not be read.
story:
  recipe:
    line: Balsa is the wood of a tree (Ochroma pyramidale), so it has no single chemical formula. Its cell walls are built from cellulose microfibrils, hemicellulose and lignin, as described for wood in general in the Wikipedia Wood article.
    parts:
      - name: Cellulose
        share: 40-50% of the cell wall
        role: Microfibrils that make up the cell wall (Wikipedia, Wood).
      - name: Hemicellulose
        share: 15-25% of the cell wall
        role: The matrix in which the cellulose microfibrils sit, impregnated with lignin (Wikipedia, Wood).
      - name: Lignin
        share: 15-30% of the cell wall
        role: Impregnates the hemicellulose matrix (Wikipedia, Wood).
      - name: Water
        share: 8-16% of the water in the cell walls
        role: Wood retains this water, which makes it softer and more pliable (Wikipedia, Wood).
  risk_groups:
    - title: For people
      lead: No hazard classification for balsa wood was found in any source read in this run.
      points:
        - label: Dust
          line: OSHA's wood dust overview says breathing wood particles from sanding and cutting may cause respiratory symptoms and cancer, but the extent of the hazard is not clearly established. No balsa-specific dust data was found, and the two NIOSH pages we tried returned errors.
    - title: Handling and drying
      lead: Balsa is not used green. WoodSolutions treats the moisture level as relevant to kiln drying.
      points:
        - label: Green moisture
          line: WoodSolutions prints a green moisture content of 200-400% and calls it very high.
        - label: Shrinkage
          line: Tangential shrinkage is 4.90% and radial shrinkage is 1.80%, as printed. The page does not give the moisture range for these figures.
        - label: Toughness
          line: WoodSolutions prints toughness as Low, up to 15 Nm, for both seasoned and unseasoned wood.
  why: Balsa, the wood of Ochroma pyramidale, is valued for its low density. Wikipedia gives a dry wood density range of 40 to 475 kg/m3, with about 160 kg/m3 typical. The High grade on Spot Material is 200 to 400 kg/m3. The 1958 Forest Products Journal article and Wikipedia both list composite cores, model structures and light-aircraft parts as its main uses. Its low density is the reason for these uses, and its low toughness and high moisture are the reasons it needs careful handling.
  uses:
    - where: Composite cores
      line: Wikipedia says more than 90% of the world's balsa wood volume is prepared into end-grain panels for the composites industry. The article lists wind turbine blades, surfboards and boat decks among the composite uses.
    - where: Model and light-aircraft structures
      line: Wikipedia lists balsa for model bridges, model buildings and model aircraft, and for components of full-size light aircraft, notably the World War II de Havilland Mosquito.
    - where: Core stock and buoyant articles
      line: The 1958 Forest Products Journal article lists core stock for doors, boat hulls, aircraft panels, wall or partition insulation, and buoyant marine articles.
  can_do:
    - label: Low density
      benchmark: density
      line: Wikipedia prints a typical dry wood density of 160 kg/m3, and WoodSolutions prints 160 kg/m3 for seasoned wood per standard. The printed range runs from 40 to 475 kg/m3.
    - label: Strength in bending, High grade
      benchmark: flexural_strength
      line: Spot Material prints a modulus of rupture of 28 to 70 MPa for the High grade (200 to 400 kg/m3). The same page prints a flexural strength of 350 MPa, which we did not use because it does not match its own range.
    - label: Heat conduction, High grade
      benchmark: thermal_conductivity
      line: Spot Material prints a thermal conductivity of 0.9 to 1.2 W/mK for the High grade and labels balsa a thermal insulator.
  compare: Balsa is a natural wood, so its figures depend on the density class and the grade. For the High grade, Spot Material prints a density of 200 to 400 kg/m3, a modulus of rupture of 28 to 70 MPa and a thermal conductivity of 0.9 to 1.2 W/mK. The 1958 article and WoodSolutions give figures for other density classes, but they do not print test conditions. The table compares density, bending strength and thermal conductivity, the three figures that the sources print on the same basis.
  compare_rows:
    - label: Density, High grade
      benchmark: density
    - label: Bending strength, High grade
      benchmark: flexural_strength
    - label: Thermal conductivity, High grade
      benchmark: thermal_conductivity
  handling:
    - Balsa is dried before use. WoodSolutions prints a green moisture content of 200-400% and relates it to kiln drying.
    - Dimensions change as the wood dries. WoodSolutions prints tangential shrinkage of 4.90% and radial shrinkage of 1.80%.
    - Toughness is low, up to 15 Nm as printed by WoodSolutions, so avoid impact loads that the wood cannot absorb.
  good_for:
    - Low-density cores. Wikipedia says most balsa volume goes into end-grain composite panels.
    - Model and light-aircraft structures, as listed by Wikipedia and the 1958 Forest Products Journal article.
  watch_out:
    - Green moisture of 200-400% means the wood must be dried, and dimensions change as it dries (WoodSolutions).
    - Toughness is low, up to 15 Nm as printed by WoodSolutions.
    - 'Supply: Wikipedia gives two Ecuador shares that disagree (95% or more and 70% or more).'
  verdict: Balsa is a low-density natural wood with a broad range of printed figures. The values are useful for choosing a density class, but the sources read here do not give test conditions for most of them, so check the grade before design use.