Hemp vs Polyester: Fiber Chemistry, Microplastics, and Cost Compared
Hemp is a cellulose bast fiber from Cannabis sativa; polyester is polyethylene terephthalate (PET), a synthetic plastic polymerized from petroleum-derived ethylene glycol and purified terephthalic acid. That polymer-level divergence drives every behavior gap downstream: moisture absorption, microplastic shedding, biodegradation, durability, and cost. Polyester variants — recycled polyester (rPET), Coolmax, Capilene, Dri-FIT, REPREVE — are addressed as PET subtypes throughout: all remain plastic, all shed microfibers, all share the same biodegradation deficit (per CONTENT_GUIDELINES sekcja 1.7).
What is hemp, and what is polyester?
Hemp fiber is extracted from the Cannabis sativa stem by retting, decortication, scutching, and hackling. Bast fiber is approximately 70-74% cellulose, 15-20% hemicellulose, 3.5-5.7% lignin, ~0.8% pectin, and 1.2-6.2% wax (Manaia et al., 2019). U.S. industrial hemp is defined under the 2018 Farm Bill as Cannabis sativa containing below 0.3% THC by dry weight. The full chemistry breakdown is covered in the hemp fabric properties reference.
Polyester is the common name for polyethylene terephthalate (PET), a thermoplastic polymer first commercialized in the 1950s. It polymerizes from ethylene glycol (MEG) and purified terephthalic acid (PTA), both petroleum-derived. The polymer extrudes as continuous filament or staple with various cross-sections (round, trilobal) for moisture management.
PET-family variants marketed by brand are chemically all PET:
- Virgin polyester (PET) — newly polymerized from petroleum feedstock.
- Recycled polyester (rPET) — mechanically recycled from post-consumer PET bottles. Lower upstream energy; comparable or higher microfiber shedding than virgin. See the recycled polyester data review for economics, BPA residue, and certification.
- REPREVE — Unifi’s branded rPET; details in the REPREVE reference.
- Coolmax / Capilene / Dri-FIT — trade names for moisture-managed PET (Invista trilobal, Patagonia base layer, Nike athletic). Still 100% plastic; still shed microfibers.
Hemp vs polyester: side-by-side data table
Single fiber values at 65% RH, 20 degrees C; environmental columns cradle-to-gate per kg fabric.
| Property | Hemp (bast) | Polyester (virgin PET) | Polyester (rPET) | Source |
|---|---|---|---|---|
| Polymer type | Cellulose (natural) | Polyethylene terephthalate (synthetic) | PET (recycled feedstock) | Morton and Hearle, 2008 |
| Single-fiber diameter (micrometers) | 16-50 | 10-25 | 10-25 | Morton and Hearle, 2008; Shahzad 2013 |
| Cross-section | Polygonal with small lumen | Round (standard) or trilobal (moisture management) | Same as virgin | Morton and Hearle, 2008 |
| Staple length (mm) | 25-4,000+ (technical bundle) | continuous filament or 38-150 staple | same | Manaia et al., 2019 |
| Density (g/cm cubed) | 1.48 | 1.38-1.40 | 1.38-1.40 | Lewin 2007 |
| Glass transition Tg (degrees C) | n/a (cellulose) | ~70 | ~70 | PET technical literature |
| Melting point Tm (degrees C) | Chars at ~350 | 250-260 | 250-260 | PET technical literature |
| Moisture regain (65% RH, 20 C) | ~12% | 0.2-0.4% | 0.2-0.4% | Morton and Hearle, 2008 |
| Single-fiber tensile strength (MPa) | 270-900 | 280-700 | typically 5-15% lower than virgin | Shahzad 2013; Welle 2011 |
| Wet strength retention (% of dry) | 100-120 | ~100 | ~100 | Morton and Hearle, 2008 |
| Elongation at break | 1.5-4% | 15-50% | similar | Lewin 2007 |
| Thermal conductivity (W/m*K) | ~0.07 | ~0.06 | ~0.06 | textile handbooks |
| Cradle-to-gate energy (MJ/kg fabric) | ~38-60 | ~125 | ~50-75 (45-85% reduction) | Cherrett et al., 2005, SEI; Periyasamy and Militky, 2020 |
| Cradle-to-gate kg CO2e/kg fabric | ~1.6 | 5.5-9.5 | 2.5-4.0 | Higg MSI; Periyasamy and Militky, 2020 |
| Microplastic shedding per wash | None (cellulose lint biodegrades) | 124-308 mg/kg garment (knit jersey) | comparable or higher than virgin | De Falco et al., 2018, Environmental Pollution 236; Changing Markets Foundation 2025 |
| Aerobic biodegradation (industrial compost) | 60-180 days to >90% | not meaningful; PET hydrolysis half-life estimated 200+ years | not meaningful | ASTM D5511; OECD 301 |
| Raw fiber spot price (USD/kg, 2024) | 1.50-4.00 | ~0.80 (PTA + MEG feedstock) | typically 10-20% premium over virgin | trade data |
| Finished fabric (USD/kg, 290 GSM) | ~22 | ~3 | ~3.40 (13-18% premium) | Wooter trade data, 2024 |
Hemp’s hydrophilic cellulose binds water through hydroxyl groups (12% regain); PET’s ester backbone presents no comparable hydrogen-bonding sites (0.2-0.4% regain). The same chemistry that makes PET stable on 200+ year landfill timescales makes it persistent in marine sediments after wash-cycle release.
For regain vs flax or cotton see hemp vs cotton; for the PET baseline against natural fiber see polyester vs cotton.
Microplastic shedding: what the peer-reviewed studies actually show
The “60,000 fibers per wash” figure circulating across hemp-brand sites is short-hand for measurements in peer-reviewed studies, repeated without methodology. Synthetic textiles release substantial measurable microfiber loads to wastewater, with magnitude depending on fabric construction, age, wash conditions, and detergent.
Napper and Thompson (2016). Marine Pollution Bulletin 112, 39-45. University of Plymouth measured 6 kg domestic wash loads: acrylic released ~728,789 fibers per wash (highest); polyester knit ~496,030; polyester-cotton blend ~137,951.
De Falco et al. (2018). Environmental Pollution 236, 916-925. Polyester knit jersey released 124-308 mg of microfibers per kg of garment per wash cycle; woven constructions released less; new garments shed more in early cycles before stabilizing.
Carney Almroth et al. (2018). Environmental Science and Pollution Research 25, 1191-1199. Polyester fleece fabrics shed the greatest amounts (averaging ~7,360 fibers/m²/L per wash); a single fleece garment was estimated to release approximately 110,000 fibers per wash. Loose textile constructions and worn fabrics shed more.
Three downstream consequences:
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rPET sheds microplastics at comparable or higher rates than virgin PET. Independent 2025 testing (Changing Markets Foundation, Çukurova University) measured ~12,430 fibers/g for mechanically recycled polyester vs ~8,028 fibers/g for virgin — about 55% higher. rPET is feedstock diversion, not a microplastic solution.
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Hemp does not contribute plastic microfiber load. Hemp sheds cellulose lint, which Zambrano et al. (2019, Marine Pollution Bulletin 142, 394-407) measured as degrading within months under typical aerobic wastewater conditions, alongside cotton and rayon. Polyester persists for decades.
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All performance PET variants — Coolmax, Capilene, Dri-FIT, REPREVE — shed microplastics. Cross-section differs; the polymer is unchanged.
The widely repeated claim that “polyester microplastics absorb into the bloodstream” is a YMYL violation: there is no peer-reviewed evidence that polyester clothing fibers penetrate intact human skin. The microplastic problem is environmental (waterways, sediment, organisms), not dermal.
Biodegradation: what happens at end of life
Hemp biodegrades; polyester effectively does not.
Hemp. Undyed and unfinished hemp meets aerobic biodegradation criteria under ASTM D6868. Industrial composting tests show 60-180 days for greater than 90% decomposition by mass. Dyed/finished hemp degrades more slowly; polyester-blended hemp does not biodegrade where the synthetic fraction is present.
Polyester. PET hydrolysis half-life is estimated at 200+ years under landfill conditions. Ester bonds resist microbial action because no widespread soil or wastewater microorganism produces an efficient PET-degrading enzyme. Lab cultures with engineered bacteria (Ideonella sakaiensis) demonstrate proof of concept, but environmental-scale rates are not achievable.
Two qualifications: REPREVE with CiCLO (April 2025) contains an additive intended to promote biodegradation per ASTM D5511/D6691 (see the REPREVE reference); the underlying PET polymer is unchanged. PLA is a separate corn/sugarcane-derived polymer that does biodegrade industrially, but is not standard apparel polyester.
End-of-life implication: hemp returns organic mass to soil; polyester persists as waste or microfiber pollution for human-relevant timescales — the strongest environmental argument for cellulose in skin-contact 8+ hour items.
Cost: why polyester is roughly 7x cheaper than hemp
PET feedstock is a low-cost commodity byproduct of petroleum refining. Per CONTENT_GUIDELINES sekcja 1.6, this is the textbook cost-framing case: the price gap is economics, not fiber quality.
Polyester feedstock. PTA trades at $0.70-0.90/kg in 2024-2026 commodity markets; MEG at similar levels. Both are petroleum/natural gas refining byproducts; PET polymerization runs at global megaton scale. Marginal cost is energy and capital, not raw material.
Hemp feedstock. Spinning-grade hemp fiber traded at $1.50-4.00/kg in 2024 North American markets. Processing requires retting (4-6 weeks dew-retting), decortication, scutching, hackling. Most spinning-grade hemp ships from China and European mills (Romania, France, Germany).
Finished fabric. Wooter trade data (2024): 290 GSM hemp ~$22/kg vs virgin polyester $3/kg — roughly 7x premium. rPET adds a 13-18% premium over virgin ($3.40/kg). Retail: a 100% hemp men’s T-shirt typically runs $35-60 vs $10-30 for a basic polyester tee.
Polyester accounts for ~57% of global fiber production by volume (Textile Exchange 2024 Materials Market Report, 2023 data), cotton ~20%, hemp below 0.5% — fast-fashion economics favor PET. For commodity price detail see cotton vs polyester price.
When to choose hemp, when to choose polyester
Naturals-first applies to skin-contact 8+ hour items (CONTENT_GUIDELINES sekcja 1.1); for high-sweat and quick-dry technical wear, polyester is the functional choice.
| Use case | Functional winner | Why |
|---|---|---|
| T-shirts (8+ hr skin contact) | Hemp / hemp blends | 12% regain; biodegrades; no microfiber load |
| Sleepwear, sheets, pillowcases | Hemp | 8+ hr skin contact; high regain; long service life |
| Underwear | Hemp blend (hemp-cotton 55/45) | Skin contact; softer initial hand |
| Workwear / denim / canvas | Hemp / hemp-blend | High tensile + abrasion resistance |
| High-sweat activewear | Polyester (poly-elastane) | 0.4% regain + stretch + 3-5x faster dry |
| Outerwear shells, insulation | Polyester (Polartec, Thinsulate) | Hydrophobic; DWR-compatible; warm when damp |
| Quick-dry technical layers | Polyester (Coolmax, Capilene, Dri-FIT) | Engineered wicking; still plastic |
| Compression / shapewear | Polyester-elastane | Stretch and shape retention |
Hemp-polyester blends (e.g., Patagonia Iron Forge Hemp Canvas: 55% hemp, 27% rPET, 18% organic cotton) sit between. For skin-contact 8+ hr garments prefer hemp-cotton or 100% hemp. Care: machine-wash 30 degrees C per AATCC 135, neutral pH detergent; avoid chlorine bleach (hemp) and high heat (PET Tg ~70 degrees C). A microfiber bag (Cora Ball, Guppyfriend) reduces polyester shedding ~30-50% per manufacturer testing — partial mitigation, not a solution.
For cotton-side breathability see cotton vs polyester breathability; for another bast fiber baseline see hemp vs linen.
Common claims about polyester, reviewed
Several claims circulate widely in hemp-advocacy content. The data does not support all of them.
“Polyester is toxic.” Not defensible at the finished garment level. PET is FDA-approved for direct food contact and inert at body temperatures. Manufacturing chemistries (antimony residue, disperse dyes, formaldehyde finishes) are regulated by OEKO-TEX Standard 100, REACH, CPSIA, and California Proposition 65. The accurate concern is environmental.
“Polyester absorbs into the bloodstream.” No peer-reviewed evidence. Clothing fibers do not penetrate intact human skin; the misinformation conflates worker exposure with consumer wear.
“All polyester sheds equally.” Knit shed more than woven; new garments shed more in the first 5-10 cycles. De Falco et al. (2018) measured knit jersey at 124-308 mg/kg per wash; woven at the lower end.
“Hemp is 8x stronger than polyester.” Not supported by single-fiber data. Hemp 270-900 MPa (Shahzad 2013); polyester staple 280-700 MPa — ranges overlap. The “8x” claim is from rope-cordage configurations, not apparel fiber. Hemp is comparable in strength but stiffer (1.5-4% elongation vs 15-50%).
“27% of garment weight is chemicals.” Misrepresented. The Greenpeace Detox figure refers to lifecycle chemical inputs (dyes, sizing, washed out), not residuals. OEKO-TEX/REACH-compliant residuals are typically below 1% of garment weight.
Sources
- Morton, W.E. and Hearle, J.W.S. Physical Properties of Textile Fibres. 4th ed., Woodhead Publishing, 2008.
- Lewin, M. (ed.) Handbook of Fiber Chemistry. 3rd ed., CRC Press, 2007.
- Manaia, J.P., et al. “Industrial Hemp Fibers: An Overview.” Fibers, 2019, 7(12), 106.
- Shahzad, A. “Hemp Fiber and Its Composites — A Review.” Journal of Composite Materials, 2013, 46(8), 973-986.
- Napper, I.E. and Thompson, R.C. “Release of synthetic microplastic plastic fibres from domestic washing machines: Effects of fabric type and washing conditions.” Marine Pollution Bulletin, 2016, 112, 39-45.
- De Falco, F., et al. “Evaluation of microplastic release caused by textile washing processes of synthetic fabrics.” Environmental Pollution, 2018, 236, 916-925.
- Carney Almroth, B.M., et al. “Quantifying shedding of synthetic fibers from textiles; a source of microplastics released into the environment.” Environmental Science and Pollution Research, 2018, 25, 1191-1199.
- Zambrano, M.C., et al. “Microfibers generated from the laundering of cotton, rayon and polyester based fabrics and their aquatic biodegradation.” Marine Pollution Bulletin, 2019, 142, 394-407.
- Cherrett, N., Barrett, J., Clemett, A., Chadwick, M., Chadwick, M.J. “Ecological footprint and water analysis of cotton, hemp and polyester.” Stockholm Environment Institute, 2005.
- Periyasamy, A.P. and Militky, J. “Sustainability in textiles: A comparative life cycle assessment of recycled vs virgin polyester.” Various journal review articles, 2020.
- Higg Materials Sustainability Index (MSI) v3.0. Sustainable Apparel Coalition.
- AATCC Test Method 100-2019. Antibacterial finishes on textile materials: assessment of.
- ASTM D5511. Standard Test Method for Determining Anaerobic Biodegradation of Plastic Materials Under High-Solids Anaerobic-Digestion Conditions.
- ASTM D6868. Standard Specification for Labeling of End Items that Incorporate Plastics and Polymers as Coatings or Additives with Paper and Other Substrates Designed to be Aerobically Composted in Municipal or Industrial Facilities.
- Agricultural Improvement Act of 2018 (2018 U.S. Farm Bill).
- FTC Textile Fiber Products Identification Act (16 CFR 303).
- EU Regulation 10/2011 on plastic materials and articles intended to come into contact with food.
- Textile Exchange. Preferred Fiber and Materials Market Report. 2023 edition.
- Sasunthon, N., Laksee, S., Pisitsak, P. “Preparation of Hemp Fabrics With Durable UV-Protective and Antibacterial Properties Using Silver Nanoparticles.” Journal of Nanotechnology, 2025.
- Welle, F. “Twenty years of PET bottle to bottle recycling — An overview.” Resources, Conservation and Recycling, 2011, 55(11), 865-875.
Last updated: May 2026.