Kevlar para-aramid fibre PPD-T (Kevlar)

spore: profile
id: kevlar
spore_version: 0.2
family: glass-and-composites
name: Kevlar para-aramid fibre
abbreviation: PPD-T (Kevlar)
role: high-strength fibre
category: polymers
type: aramids
summary: |
  Kevlar is a para-aramid fibre made from poly(p-phenylene terephthalamide). Its rigid, rod-like chains are held together by hydrogen bonds, which gives a tensile strength about five times that of steel by weight. It resists heat without melting, but it discolours and loses strength under ultraviolet light. In low Earth orbit on the MISSE 2 tray, PPDT eroded by 6.28e-25 cm3 per oxygen atom, a low erosion yield for a polymer in that list.
best_for: Light, strong fibre for body armour, cut-resistant gear and ropes, where the fibre is shielded from sunlight
weakest_at: Ultraviolet light, which discolours it and cuts its mechanical strength; and low stiffness in compression
identity:
  formula: Poly(p-phenylene terephthalamide), repeat unit C14H10N2O2
  source: nasa-tm
  where: Table IV (PPD-T repeat unit C14H10N2O2, 238.2452 g/mol); DuPont guide, Section I (aromatic polyamide)
tags:
  environments:
    - low-earth-orbit
  stresses:
    - atomic-oxygen
    - uv
    - thermal-cycling
  applications:
    - habitats-and-suits
    - structures
properties:
  - benchmark: atomic_oxygen_erosion_yield
    label: Atomic oxygen erosion yield, MISSE 2 flight
    value: 6.28e-25
    unit: cm3/atom
    scope: material
    conditions:
      exposure: low Earth orbit, ISS MISSE 2 PEACE tray 1, 2001-08-16 to 2005-07-30
      fluence: 8.43e21 atoms/cm2
      solar: 5000-6700 equivalent sun hours
      thermal_cycling: '-30 to 40 degC nominal base-plate range'
    method: Flight-measured erosion yield as printed in the NASA predictive-tool report
    status: flight
    source: nasa-tm
    where: Table I (MISSE 2 PEACE polymers erosion yield data, row PPDT (Kevlar)); exposure in section 2.1
  - benchmark: density
    label: Density, Kevlar 29 and 49 yarn
    value: 1.44
    unit: g/cm3
    scope: material
    conditions:
      basis: yarn density as printed for both Kevlar 29 and Kevlar 49
    method: Typical value printed in the DuPont technical guide table
    status: ground
    source: dupont-guide
    where: Table II-1, Density row
  - benchmark: density
    label: Density, PPDT by MISSE 2 measurement
    value: 1.4422
    unit: g/cm3
    scope: material
    conditions:
      basis: measured density of the MISSE 2 PPDT sample as printed
    method: Value from the NASA erosion report density table
    status: ground
    source: nasa-tm
    where: Table II (density and ash content, row PPDT (Kevlar))
  - benchmark: ultimate_tensile_strength
    label: Breaking tenacity, Kevlar 29 yarn
    value: 2920
    unit: MPa
    scope: material
    conditions:
      basis: straight test on conditioned yarn, 1,500 denier, standard modulus; printed as 23.0 g/d and 424,000 psi
    method: Typical value printed in DuPont technical guide, shown with the MPa conversion as printed
    status: ground
    source: dupont-guide
    where: Table II-1, Breaking Tenacity row (Kevlar 29 column)
  - benchmark: ultimate_tensile_strength
    label: Breaking tenacity, Kevlar 49 yarn
    value: 3000
    unit: MPa
    scope: material
    conditions:
      basis: straight test on conditioned yarn, 1,140 denier, high modulus; printed as 23.6 g/d and 435,000 psi
    method: Typical value printed in DuPont technical guide, shown with the MPa conversion as printed
    status: ground
    source: dupont-guide
    where: Table II-1, Breaking Tenacity row (Kevlar 49 column)
  - benchmark: ultimate_tensile_strength
    label: Tensile strength, single Kevlar 29 fibre (laboratory)
    value: 3040
    unit: MPa
    scope: material
    conditions:
      basis: single-fibre tensile test, printed as 3.04 GPa plus or minus 0.31 GPa
    method: Measured value printed in the single-fibre study (converted from GPa as printed)
    status: ground
    source: cimav-k29
    where: Results, tensile strength row
  - benchmark: elastic_modulus
    label: Tensile modulus, Kevlar 29 yarn
    value: 70500
    unit: MPa
    scope: material
    conditions:
      basis: straight test on conditioned yarn, standard modulus; printed as 555 g/d and 10.2e6 psi
    method: Typical value printed in DuPont technical guide
    status: ground
    source: dupont-guide
    where: Table II-1, Tensile Modulus row (Kevlar 29 column)
  - benchmark: elastic_modulus
    label: Tensile modulus, Kevlar 49 yarn
    value: 112400
    unit: MPa
    scope: material
    conditions:
      basis: straight test on conditioned yarn, high modulus; printed as 885 g/d and 6.3e6 psi
    method: Typical value printed in DuPont technical guide
    status: ground
    source: dupont-guide
    where: Table II-1, Tensile Modulus row (Kevlar 49 column)
  - benchmark: elastic_modulus
    label: Young's modulus, single Kevlar 29 fibre (laboratory)
    value: 83.78
    unit: GPa
    scope: material
    conditions:
      basis: single-fibre tensile test, printed as 83.78 plus or minus 7.12 GPa
    method: Measured value printed in the single-fibre study
    status: ground
    source: cimav-k29
    where: Results, Young's modulus row
  - benchmark: elongation
    label: Elongation at break, Kevlar 29 yarn
    value: 3.6
    unit: '%'
    scope: material
    conditions:
      basis: straight test on conditioned yarn
    method: Typical value printed in DuPont technical guide
    status: ground
    source: dupont-guide
    where: Table II-1, Elongation at Break row (Kevlar 29 column)
  - benchmark: elongation
    label: Elongation at break, Kevlar 49 yarn
    value: 2.4
    unit: '%'
    scope: material
    conditions:
      basis: straight test on conditioned yarn
    method: Typical value printed in DuPont technical guide
    status: ground
    source: dupont-guide
    where: Table II-1, Elongation at Break row (Kevlar 49 column)
  - benchmark: moisture_absorption
    label: Equilibrium moisture regain, PPD-T fibre
    value: 5
    unit: '%'
    scope: material
    conditions:
      basis: equilibrium moisture regain at 55% relative humidity
    method: Value printed in the PolyOne/Fiber-Line Kevlar para-aramid datasheet (both standard and high modulus grades)
    status: ground
    source: polyone-kevlar
    where: Kevlar para-aramid data table, Moisture Regain row
  - benchmark: moisture_absorption
    label: Equilibrium moisture from bone-dry yarn, Kevlar 29
    value: 4.5
    unit: '%'
    scope: material
    conditions:
      basis: bone-dry yarn conditioned at 75 degF (24 degC) and 55% RH
    method: Value printed in DuPont technical guide, moisture levels
    status: ground
    source: dupont-guide
    where: Table II-1, Moisture Levels row (equilibrium from bone-dry yarn)
  - benchmark: specific_heat
    value: 0.34
    unit: cal/g x degC
    scope: material
    conditions:
      basis: at 77 degF (25 degC), as printed in the DuPont table
    method: Value printed in DuPont technical guide; printed unit kept
    status: ground
    source: dupont-guide
    where: Table II-1 Thermal Properties, specific heat row (At 77 degF)
  - benchmark: decomposition_temperature
    label: Decomposition temperature in air (no melting point)
    value: 427
    value_high: 482
    bound: range
    unit: degC
    scope: material
    conditions:
      basis: decomposes rather than melts; range measured at a 10 degC per minute temperature rise in air, nitrogen about 538 degC
    method: Range printed in the DuPont guide
    status: ground
    source: dupont-guide
    where: Section 2, Decomposition Temperature; Table II-1 Decomposition Temperature row
  - benchmark: molar_mass
    label: Molar mass of repeat unit
    value: 238.2452
    unit: g/mol
    scope: material
    conditions:
      repeat_unit: C14H10N2O2
    method: Value printed in the NASA table of polymer chemical structure
    status: ground
    source: nasa-tm
    where: Table IV, row PPD-T (Kevlar)
corrosion:
  - environment: Ultraviolet light and sunlight
    headline: 'UV is Kevlar''s main weakness: it yellows and then browns, and mechanical strength falls with long exposure.'
    effect: Unprotected yarn discolours from yellow to brown after prolonged exposure, and extended UV exposure can cut mechanical properties depending on wavelength, time and intensity. Degradation needs oxygen, and it is not increased by moisture or sulfur dioxide. The overlap of the fibre absorption spectrum and sunlight lies between 300 and 450 nm, so that range must be excluded for protection.
    rating: severe
    conditions:
      exposure: sunlight or UV, unprotected, in the presence of oxygen
      wavelength_range: 300 to 450 nm overlap with sunlight
    source: dupont-guide
    where: Section 2, Effect of UV Light on Kevlar, and Figure 2.11
  - environment: Humid air
    headline: Kevlar takes up moisture, but its tensile properties are virtually unaffected by moisture content.
    effect: Equilibrium moisture regain is about 5.0% at 55% RH and rises linearly with relative humidity. Bone-dry Kevlar 29 reaches 4.5% at equilibrium. The guide states that tensile properties are virtually unaffected by moisture content.
    rating: low
    conditions:
      humidity: 55% RH equilibrium; linear with RH
      temperature: 24 degC
    source: polyone-kevlar
    where: Kevlar para-aramid data, Moisture Regain row; DuPont guide Section 2, Moisture Regain
  - environment: Heat (thermal ageing)
    headline: Strength drops about 10 to 20 percent at once when heated, then keeps falling with time at high temperature.
    effect: Per Wikipedia, tensile strength falls by 10 to 20 percent at higher temperatures straight away, and strength keeps reducing over hours. Enduring 160 degC for 500 hours reduces strength by about 10 percent. The fibre keeps strength down to cryogenic temperatures.
    rating: moderate
    conditions:
      example: 160 degC for 500 hours, about 10 percent loss
      note: secondary source; not the DuPont test
    source: wiki-kevlar
    where: Thermal properties section
  - environment: Strong acids and alkalis at high temperature
    headline: Kevlar holds strength in neutral water but degrades in strong acids and hot alkalis.
    effect: At neutral pH the filament tenacity stays unchanged after 200 days at 65 degC. Acidic conditions cause more severe degradation than basic ones, and the guide's table lists degradation in formic acid at 90 percent and in hydrochloric acid at 10 percent and 160 degF (71 degC). Sodium hydroxide at 10 percent and 210 degF (99 degC) degrades the fibre.
    rating: moderate
    conditions:
      basis: guide table of chemical exposures; strength loss read as Degraded in the table
    source: dupont-guide
    where: Section 2 chemical resistance tables; Chemical Compatibility text
risks:
  hazards:
    - text: 'PubChem aggregated GHS for p-phenylenediamine (Kevlar monomer, CID 7814; 597 company reports): H301 toxic if swallowed, H311 toxic in contact with skin, H331 toxic if inhaled (each 99.7%); H317 may cause an allergic skin reaction; H319 causes serious eye irritation; H370 causes damage to organs (38.9%); H400 and H410 very toxic to aquatic life. Signal word Danger.'
      ghs:
        - H301
        - H311
        - H331
        - H317
        - H319
        - H370
        - H400
        - H410
      source: pubchem-kevlar-monomers
      where: Safety and Hazards, GHS Classification (CID 7814)
    - text: 'PubChem aggregated GHS for terephthaloyl chloride (Kevlar monomer, CID 7488; 2263 company reports): 88.7% of reports say it does not meet GHS criteria. Where classified: H314 causes severe skin burns and eye damage (11.2%); H331 toxic if inhaled (11.1%). Signal word Danger.'
      ghs:
        - H314
        - H331
      source: pubchem-kevlar-monomers
      where: Safety and Hazards, GHS Classification (CID 7488)
    - text: 'Fibre dust and particulates: the DuPont SDS gives the product hazard as combustible dust. Small particles from processing or handling may form combustible dust concentrations in air. Fibre fly and dust can irritate the eyes, nose and airways, and rubbing fibre particulates on skin can cause transitory mild redness or itching. The SDS does not describe fibrils as a separate hazard.'
      ghs: []
      source: sds-kevlar
      where: Section 2 Hazard statements; Handling (Personnel) row
    - text: 'Dust and fibre exposure limits from the SDS: DuPont AEL 2 RFP/cc for respirable fibres and 5 mg/m3 for non-fibrous dust (8 and 12 h TWA); OSHA PEL 5 mg/m3 respirable fraction and 15 mg/m3 total dust; ACGIH TLV 3 mg/m3 respirable and 10 mg/m3 inhalable.'
      ghs: []
      source: sds-kevlar
      where: Section 8, Exposure Limit Values
    - text: 'Fire: the SDS gives an ignition temperature of does not ignite and a decomposition temperature above 300 degC. Burning gives carbon dioxide, nitrogen oxides, hydrogen cyanide, ammonia, aldehydes and hydrocarbons. Firefighters need self-contained breathing apparatus.'
      ghs: []
      source: sds-kevlar
      where: Fire-fighting measures; Flammability and Decomposition rows
  failure_risks:
    - mode: UV discolouration and strength loss
      trigger: Unprotected sunlight or UV exposure in the presence of oxygen
      consequence: Yellowing, then browning, and loss of mechanical properties with long exposure
      severity: moderate
      source: dupont-guide
      where: Section 2, Effect of UV Light on Kevlar
    - mode: Thermal decomposition at high temperature
      trigger: Heating above about 427 degC in air
      consequence: Kevlar does not melt; it decomposes between 427 and 482 degC in air
      severity: moderate
      source: dupont-guide
      where: Section 2, Decomposition Temperature
    - mode: Chemical attack
      trigger: Strong formic or hydrochloric acid, or hot sodium hydroxide
      consequence: Breaking strength falls with the exposure table's degradation rating
      severity: moderate
      source: dupont-guide
      where: Chemical resistance tables; Chemical Compatibility text
  side_effects: []
  handling:
    - text: Shield the fibre from sunlight and UV; the guide says the 300 to 450 nm range must be excluded for outdoor use without protection.
      source: dupont-guide
      where: Section 2, Effect of UV Light on Kevlar
    - text: 'Avoid dust formation: use exhaust ventilation or vacuum cleaning rather than dry sweeping, wear safety glasses with side shields, and use a certified respirator where the exposure limit is exceeded.'
      source: sds-kevlar
      where: Handling (Personnel), Spill Cleanup and Section 8 Exposure Controls
  mitigations:
    - text: Use UV-blocking protection or stow the fibre in darkness; discolouration of fresh yarn from ordinary room light is normal and is not degradation.
      source: dupont-guide
      where: Section 2, Effect of UV Light on Kevlar
uses:
  - application: habitats-and-suits
    device: Body armour and ballistic vests
    example: Kevlar is a well-known component of personal armour, including helmets and ballistic vests; the US military PASGT helmet and vest relied on it.
    source: wiki-kevlar
    where: Applications section (personal armour)
  - application: habitats-and-suits
    device: Cut-resistant gloves and protective clothing
    example: Kevlar is used in gloves, sleeves and jackets to protect against cuts, abrasions and heat.
    source: wiki-kevlar
    where: Applications section (protective clothing)
  - application: structures
    device: Composite reinforcement
    example: Kevlar is spun into ropes or fabric, or used as an ingredient in composite components, and is used for mooring lines.
    source: wiki-kevlar
    where: Lead paragraphs; applications section
  - application: propulsion-and-tanks
    device: Stuffed Whipple shield on a robotic spacecraft propellant tank
    example: The PACE tank ram-direction shield used six layers of Nextel and six layers of Kevlar between two 0.20 cm aluminium plates with a 4 cm standoff, chosen to balance risk and mass.
    source: ntrs-whipple
    where: Text after the case comparison table, selected ram shield configuration (Case 6)
supply:
  - subject: Kevlar (PPD-T) production
    abundance: Not sourced. Feedstock is the two monomers, p-phenylenediamine and terephthaloyl chloride (Wikipedia).
    producers: []
    critical_lists: []
    recycling: Not sourced.
    substitutes:
      - Twaron, a fibre with the same chemical structure developed by Akzo, produced by Teijin Aramid (Wikipedia).
    source: wiki-kevlar
    where: Lead paragraphs; Production section
media: []
documents:
  - title: 'NASA/TM-2008-215490: Atomic Oxygen Erosion Yield Predictive Tool for Spacecraft Polymers in Low Earth Orbit'
    type: report
    url: https://ntrs.nasa.gov/citations/20090011780
    year: 2008
  - title: DuPont Kevlar Technical Guide (copy hosted at r-g.de)
    type: datasheet
    url: https://www.r-g.de/wiki/images/e/ec/Td_en_Kevlar_guide.pdf
    year: 2010
  - title: PolyOne / Fiber-Line Kevlar para-aramid datasheet
    type: datasheet
    url: https://automotive.polyone.com/sites/default/files/2021-06/fl.us-.datasheet-kevlar-para-aramid.pdf
    year: 2021
  - title: The tensile behavior of Kevlar 29 fibers (CIMAV repository)
    type: paper
    url: https://cimav.repositorioinstitucional.mx/jspui/bitstream/1004/1347/1/The%20tensile%20behavior%20of%20Kevlar%2029%20fibers.pdf
    year: 2014
  - title: KEVLAR Para-aramid Safety Data Sheet, Version 8.1 (copy hosted by Easy Composites)
    type: sds
    url: https://media.easycomposites.co.uk/datasheets/Dupont-Kevlar-SDS-Ver8_1-23Mar2023.pdf
    year: 2024
  - title: Application of Stuffed Whipple Shield to Robotic Spacecraft (NTRS 20230015317)
    type: paper
    url: https://ntrs.nasa.gov/citations/20230015317
    year: 2023
  - title: 'PubChem GHS classification: p-phenylenediamine (CID 7814) and terephthaloyl chloride (CID 7488)'
    type: database
    url: https://pubchem.ncbi.nlm.nih.gov/compound/7814
    year: 2026
gaps:
  - No Kevlar 149 value found in any fetched page; the DuPont guide copy has Kevlar 29 and 49 only. Kevlar 149 is named in Wikipedia as the highest-tenacity grade, without numbers.
  - No PubChem record exists for the polymer (searches for Kevlar and poly(p-phenylene terephthalamide) returned none), so hazards use the two monomers and the DuPont SDS for Kevlar. The fibrils hazard is not described separately in any source read.
  - The Stuffed Whipple paper NTRS 20230015317 was read and is used for the layup only, not for property values. NTRS 20250001790 (a basalt paper) would not download and is not used.
  - No tether or space-tether source was read for Kevlar; the tether use is not included.
  - No producer list or production volumes were found; supply is limited to the monomers and the Twaron substitute.
  - The decomposition-temperature and molar-mass names are not in property-canon.yaml; they are used as short snake_case names.
  - Vacuum outgassing and total radiation dose for Kevlar were not read; the passport lists those stresses but no result for them was fetched.
  - Monomer composition by weight is calculated from the printed repeat-unit formula C14H10N2O2, not read from a source (see recipe).
sources:
  nasa-tm:
    title: Atomic Oxygen Erosion Yield Predictive Tool for Spacecraft Polymers in Low Earth Orbit
    id: NASA/TM-2008-215490 (Banks, Backus and de Groh, December 2008)
    url: https://ntrs.nasa.gov/citations/20090011780
    year: 2008
    kind: report
    license: public domain (NASA)
  dupont-guide:
    title: DuPont Kevlar Technical Guide (copy hosted at r-g.de)
    id: DuPont Kevlar aramid fiber technical guide
    url: https://www.r-g.de/wiki/images/e/ec/Td_en_Kevlar_guide.pdf
    year: 2010
    kind: datasheet
    license: copy hosted by a third party; cited, not reproduced
  polyone-kevlar:
    title: Kevlar para-aramid datasheet (Fiber-Line, PolyOne)
    id: fl.us-.datasheet-kevlar-para-aramid
    url: https://automotive.polyone.com/sites/default/files/2021-06/fl.us-.datasheet-kevlar-para-aramid.pdf
    year: 2021
    kind: datasheet
    license: supplier document, cited not reproduced
  cimav-k29:
    title: The tensile behavior of Kevlar 29 fibers
    id: CIMAV institutional repository, item 1004/1347
    url: https://cimav.repositorioinstitucional.mx/jspui/bitstream/1004/1347/1/The%20tensile%20behavior%20of%20Kevlar%2029%20fibers.pdf
    year: 2014
    kind: paper
    license: cited, not reproduced
  wiki-kevlar:
    title: 'Wikipedia: Kevlar'
    id: Kevlar
    url: https://en.wikipedia.org/wiki/Kevlar
    kind: web
    license: CC BY-SA 4.0 (cited, not reproduced)
  sds-kevlar:
    title: KEVLAR Para-aramid Safety Data Sheet, Version 8.1 (Ref. 150000002634; revision 03/23/2023)
    id: DuPont SDS, copy hosted by Easy Composites
    url: https://media.easycomposites.co.uk/datasheets/Dupont-Kevlar-SDS-Ver8_1-23Mar2023.pdf
    year: 2024
    kind: datasheet
    license: supplier safety data sheet, cited not reproduced
  ntrs-whipple:
    title: Application of Stuffed Whipple Shield to Robotic Spacecraft
    id: NASA NTRS 20230015317, 2nd International Orbital Debris Conference (2023)
    url: https://ntrs.nasa.gov/citations/20230015317
    year: 2023
    kind: paper
    license: NASA technical report, public distribution
  pubchem-kevlar-monomers:
    title: PubChem GHS classification for p-phenylenediamine and terephthaloyl chloride
    id: PubChem CID 7814 and CID 7488, read via the PUG REST API
    url: https://pubchem.ncbi.nlm.nih.gov/compound/7814
    kind: database
    license: PubChem, cited not reproduced
license: CC-BY-4.0
updated: '2026-10-19'
review:
  status: draft
  method: assistant
  checked_values: 16
  unreachable: 0
  caveats: 3
  note: Written by an AI assistant on 2026-10-19 from the NASA TM Table I, II and IV, the DuPont guide, the PolyOne datasheet, one single-fibre paper and Wikipedia. Only 5 sources were read, short of the 8 requested. Hazards and some uses are not sourced.
story:
  recipe:
    line: Kevlar is made by condensation of p-phenylenediamine with terephthaloyl chloride in solution, which gives hydrochloric acid as a byproduct (Wikipedia). The repeat unit is C14H10N2O2 (NASA Table IV). The polymer forms liquid-crystalline solutions, and drawing orients the chains along the fibre.
    parts:
      - name: p-Phenylenediamine (monomer)
        symbol: C6H8N2
        role: Diamine that forms the rigid para-phenylene and amide-N part of each repeat unit (Wikipedia).
      - name: Terephthaloyl chloride (monomer)
        symbol: C8H4Cl2O2
        role: Diacid chloride that forms the terephthalamide part; the byproduct HCl leaves in the condensation (Wikipedia).
      - name: Repeat unit
        symbol: C14H10N2O2
        share_note: molar mass 238.2452 g/mol (NASA Table IV)
        role: The polymer unit that repeats along the chain; carbon, hydrogen, nitrogen and oxygen only.
  risk_groups:
    - title: For people
      level: 0
      verdict: Hazards not checked
      lead: No safety data sheet or GHS record for Kevlar was read in this run, so no hazard classification is given.
      points:
        - label: Dust and cutting
          line: The fibre is handled as yarn or fabric. Check the supplier safety data sheet before cutting or grinding it.
        - label: Fire
          line: Kevlar does not melt. It decomposes between 427 and 482 degC in air (DuPont guide).
    - title: In the environment
      level: 1
      verdict: Sunlight is the watch point
      lead: UV is the main route to loss of strength.
      points:
        - label: UV
          line: Unprotected yarn discolours from yellow to brown and loses strength with long exposure; the 300 to 450 nm range must be excluded (DuPont guide).
        - label: Moisture
          line: Kevlar takes up about 5 percent moisture at 55 percent RH, but its tensile properties are virtually unaffected (PolyOne datasheet, DuPont guide).
  why: Kevlar is a para-aramid, so its chains are rigid and aligned, and hydrogen bonds link neighbouring chains. That gives a high strength per unit weight and a high modulus. The trade is UV sensitivity and low compressive strength. In the MISSE 2 flight test it eroded slowly under atomic oxygen, which is why it was included in the passport.
  uses:
    - where: Body armour
      line: Kevlar is a key component of personal armour, including helmets and ballistic vests, as Wikipedia records.
    - where: Protective clothing
      line: Gloves, sleeves and jackets made of Kevlar protect against cuts, abrasion and heat, and are lighter than comparable protection (Wikipedia).
    - where: Ropes and composites
      line: Kevlar is spun into ropes, used as mooring lines and as a composite ingredient (Wikipedia). Spacecraft shielding and tethers are not covered here because no source was read for them.
  can_do:
    - label: Strength
      benchmark: ultimate_tensile_strength
      line: Kevlar 29 yarn breaks at 2,920 MPa and Kevlar 49 at 3,000 MPa (DuPont guide). A single Kevlar 29 fibre measured 3.04 GPa plus or minus 0.31 GPa.
    - label: Stiffness
      benchmark: elastic_modulus
      line: Kevlar 29 yarn has a tensile modulus of 70,500 MPa and Kevlar 49 of 112,400 MPa (DuPont guide). A single Kevlar 29 fibre measured 83.78 GPa.
    - label: Flight exposure
      value: 6.28e-25 cm3/atom
      line: In low Earth orbit on MISSE 2, PPDT eroded by 6.28e-25 cm3 per atomic oxygen atom (NASA Table I).
  compare: Kevlar is strong and light for a polymer, but it is weaker in UV than many engineering plastics, and it absorbs about five percent moisture. Its atomic-oxygen erosion yield in LEO is lower than several common polymers in the same NASA table, such as polyethylene and PMMA, which makes it a credible choice for space use shielded from sunlight.
  compare_rows:
    - scope: material
      label: Strength
      benchmark: ultimate_tensile_strength
    - scope: material
      label: Stiffness
      benchmark: elastic_modulus
    - scope: material
      label: Atomic oxygen erosion
      benchmark: atomic_oxygen_erosion_yield
  handling:
    - Keep it out of sunlight and UV, or cover it with a UV blocker.
    - Expect about 5 percent moisture pickup at 55 percent RH; tensile properties are not much affected.
    - Keep it below 427 degC; it decomposes rather than melts.
  good_for:
    - Strength for weight in armour, cut-resistant gear and ropes.
    - Low atomic-oxygen erosion in LEO, measured on MISSE 2.
  watch_out:
    - UV discolours and weakens unprotected yarn.
    - Strong acids and hot alkalis degrade the fibre.
    - Compressive strength is poor (PolyOne datasheet).
  verdict: Kevlar is a strong, light, heat-tolerant fibre whose weak point is sunlight. Shield it from UV, and it performs well in orbit and in armour.