Oct 6, 2026

PU vs TPU vs PVC Coatings: Which Lasts on Bike Covers?

Supplier data: PU coatings 3,000-5,000 mm / 2-5 years vs TPU 20,000-40,000 mm / 10-15+ years. What hydrolysis is and what to specify for your climate.

Bike brands compare waterproof numbers at the sample stage. Three years later, the question is different: is the coating still flexible, or has it gone sticky, cracked and started flaking? This article looks at the published data on coating chemistry - what fails, when, and what to specify for your climate.
Key takeaways
• Coating choice decides lifespan, not just waterproofing: supplier comparison data puts PU at 3,000-5,000 mm and 2-5 years, TPU at 20,000-40,000 mm and 10-15+ years (supplier data).
• The failure mode is hydrolysis: moisture plus heat breaks down the PU polymer itself. MSR (Cascade Designs) describes it as coating breakdown due to moisture, heat and humidity, which causes the coating to become sticky and fail.
• Not all PU is equal. The American Association for Contract Textiles (ACT) ranks PU resin chemistries for hydrolysis resistance: polycarbonate, then polyether, then polyester (worst).
• The industry measures it with a standard: ISO 1419 tropical testing at 70C and 95%+ humidity, with ACT thresholds of 5 weeks (indoor) and 10 weeks (outdoor exposure class). Test weeks do not convert directly to years of service.
• PVC does not hydrolyse (ACT), but its plasticisers migrate - and the bike industry is moving away from it: Ortlieb's TIDURA fabric system is PVC-free TPU, and Vaude's waterproof panniers are PVC-free.
How we verified this
This is a data review of published sources: the ACT hydrolysis education paper and coating test guides (association-level guidance), MSR / Cascade Designs' official coating explanation, and a fabric supplier's PU-vs-TPU comparison table, clearly marked as supplier data. Where figures come from a supplier rather than an independent lab, we say so.
  1. What actually kills a coating: hydrolysis in plain terms
Hydrolysis is the chemical breakdown of a polymer caused by extended exposure to humidity and heat (ACT). PU coatings are vulnerable by their polymer chemistry - and in bike gear, the relevant environment is not only the rain outside: a cover stored on a balcony in summer, a bag in a hot car, or a cushion under body heat all sit in exactly the warm-and-damp window where PU degrades.
What it looks like when it fails: the coating film cracks, flakes off, or delaminates from the backing fabric - and per ACT, failures tend to appear across a whole production batch at once, not as isolated cases.
The resin matters more than the label PU:
Polycarbonate-based PU: highest hydrolysis resistance (highest relative cost)
Polyether-based PU: good hydrolysis resistance (mid cost)
Polyester-based PU: lowest hydrolysis resistance (lowest cost)
What it means for importers: PU coated on a spec sheet tells you very little. Ask which polyol the coating is based on, or test the specific construction.
  1. The numbers side by side: PU vs TPU (supplier data)
A fabric supplier's published comparison table gives the clearest side-by-side view of what buyers are choosing between:
Hydrostatic head: PU 3,000-5,000 mm vs TPU 20,000-40,000 mm
Expected service life: PU 2-5 years vs TPU 10-15+ years
Cold flexibility limit: PU -20C vs TPU -40C
Relative cost index: PU 1.0 vs TPU 1.2-1.5x
(Figure 1: PU vs TPU comparison chart. Pending upload - data listed above. Source: supplier data.)
The same source notes TPU needs no plasticisers and that although the roll goods cost 20-50% more, the cost per year of service can be lower (their example: about
300over3yearsversusabout300 over 3 years versus about

360 over 10+ years).
Two honest caveats: these are supplier figures, not independent lab results, and lifespan depends heavily on climate and use. A polyester-based PU in a dry, cool market can outlast a cheap TPU in a coastal one. Also, TPU is always better than PU would be an oversimplification - ACT's ranking shows the resin system, not the polymer family, decides hydrolysis resistance within PU.
What it means for importers: for covers and bags that live outdoors year-round, TPU (or high-grade polyether PU) is the defensible spec; for pack-away accessories used seasonally, a good PU can be the economical choice.
  1. Where PVC fits - and why bike brands are leaving it
PVC is the older, cheapest coating family and it does not hydrolyse (ACT). Its failure mode is different: PVC needs plasticisers to stay flexible, and those plasticisers migrate out over time, leaving the material stiff, then cracked at folds.
Two further pressures are pushing PVC out of bike gear: weight (PVC-coated fabrics are typically the heaviest option in the same abrasion class) and brand policy - Ortlieb's PVC-free TIDURA system uses TPU-coated woven fabric tested to a 100,000 mm water column, and Vaude's Aqua Back panniers are PVC-free PU-coated 1000D tarpaulin.
What it means for importers: PVC remains viable for high-wear, low-cost utility covers, but if your brand markets on material responsibility, specify PVC-free (TPU or PU) in the brief and ask for the material statement in writing.
  1. What this means for your bike range - a coating spec checklist
  1. State the chemistry, not just the family: polyether-based PU at 5,000 mm (ISO 811) beats PU coated.
  1. Match the coating to the climate: humid and hot markets need TPU or polyether PU; dry and cold markets can use PU, checking cold-flex at -20C.
  1. Ask for a hydrolysis test if the product will sit outdoors: ISO 1419 (70C / 95% RH), with the tested week count. ACT thresholds: 5 weeks indoor, 10 weeks outdoor class.
  1. Annualise the cost: a 20-50% higher roll price that doubles service life is a lower cost per year.
  1. Write the claim carefully: waterproof applies to the construction - fabric plus seams plus closure - not to the coating alone.
Limitations
The PU/TPU comparison numbers above are supplier-published data; we label them as such and recommend verifying on production lots.
ISO 1419 test weeks do not convert directly to field years (ACT states there is no direct correlation).
Climate, UV exposure and mechanical stress interact with hydrolysis; a single spec cannot describe every market.
FAQ
What is hydrolysis in coated fabrics?
A chemical breakdown of the coating polymer caused by extended exposure to humidity and heat (ACT). In polyurethane coatings it shows up as sticky, cracked or flaking films - often across an entire batch at once.
Does TPU last longer than PU on bike gear?
Supplier data suggests yes - roughly 10-15+ years versus 2-5 years, with lower cold-flex limits (-40C versus -20C). But resin chemistry and climate matter: a polyether PU can outperform a low-grade TPU.
Does PVC have the same problem?
No - PVC does not hydrolyse (ACT). Its failure is plasticiser migration: the material goes stiff and cracks at folds. It is also heavier, and premium bike brands are moving to PVC-free specifications.
How do I test a coating for humidity resistance?
Ask for ISO 1419 tropical testing: 70C at 95%+ relative humidity, with visual inspection each week. ACT thresholds are 5 weeks (indoor) and 10 weeks (outdoor exposure class); interpret results as comparative, not as a year count.
Which coating should I choose for humid climates?
For year-round outdoor exposure in humid climates, specify TPU or polyether-based PU, and verify with the supplier's hydrolysis data. For seasonal accessories stored indoors, a mid-grade PU may be sufficient.
Sourcing coated bike fabrics or covers? Send us your product, market climate and target lifespan - our team will propose coating chemistry, fabric construction and seam sealing, and build a sample in 7-12 days. Contact us at colorwaybag.com/contact-us.
References
Association for Contract Textiles - Hydrolysis: What You Need to Know. contracttextiles.org/learn/hydrolysis-what-you-need-to-know/
ACT - Coated fabric performance guidelines (indoor/outdoor, 2025). contracttextiles.org. MSR / Cascade Designs - Xtreme Shield tent coating. support.cascadedesigns.com
Fabric supplier PU vs TPU comparison guide (supplier data). fuhuangtex.com. Ortlieb - TIDURA material system (PVC-free, 100,000 mm). ortlieb.com. Vaude - Aqua Back panniers (PVC-free 1000D). vaude.com. ISO 1419 - accelerated-ageing tests.