PU vs PVC vs TPU Coating: How to Specify Water Resistance on a Bag
Most 'waterproof' bag failures are coating decisions. A plain guide to PU, PVC and TPU - what each does, where each cracks, what each costs - so the spec sheet says what you actually need.
7 min readcoatingswaterproofTPUPVC
A bag fabric without a coating absorbs water. Every polyester and nylon we sell for bag bodies is coated, and the coating - not the denier, not the fibre - decides whether the bag is shower-proof, waterproof, or a problem in January.
The three coatings
| PU (polyurethane) | PVC (vinyl) | TPU (thermoplastic PU) | |
|---|---|---|---|
| Applied as | Thin coating on the back | Thick coating or double-sided tarp | Laminated film |
| Hydrostatic head | 600-2,000 mm | Fully waterproof | > 5,000 mm |
| Seams | Sewn (leak at needle holes) | Sewn or welded | Welded or sewn + taped |
| Hand | Soft, matte back | Stiff, glossy | Smooth film; matte or gloss |
| Cold behaviour | Flexible | Stiffens, cracks below 0 C | Flexible to -20 C |
| EU retail | Fine | Often restricted | Preferred |
| Relative cost | + | + | +++ |
PU: the default
A one- to three-pass PU coating is on nearly every 600D polyester roll. It stops rain soaking through the body panel and keeps the fabric soft. It does not make a bag waterproof - water enters at seams and zips - and the industry term for it is "water-resistant". That is enough for school, business and most travel bags.
Specify the hydrostatic head: 1,000 mm is standard; 2,000 mm for outdoor daypacks.
PVC: cheap, waterproof, cold-fragile
PVC backing on 600D polyester is the lowest-cost waterproof panel and the classic school-bag base. PVC tarpaulin at 450-900 gsm is the courier-messenger and tool-bag fabric. Both are wipe-clean and weld easily.
The catch is temperature. The plasticiser that keeps PVC flexible stiffens below freezing and the coating cracks when flexed. PVC also softens and smells in car-boot heat above 60 C. And European retailers increasingly restrict it for chlorine and phthalate reasons - if you must use PVC in the EU, specify a phthalate-free grade with a REACH screening report.
Full details on the PVC coated fabric page.
TPU: waterproof without the compromises
TPU is a polyurethane film laminated to the base fabric. It is fully waterproof, welds for sealed seams, stays flexible at -20 C, contains no chlorine, and is recyclable. It is the specification behind every dry bag, roll-top and cooler liner sold in Europe.
It costs 2.5-4x PU-coated polyester and needs RF or hot-air welding equipment for sealed seams - which not every bag factory has. Our sister factory welds TPU dry bags and cooler liners in-house.
Full details on the TPU laminated fabric page.
Decision rules we use
- Warm market, cost-driven, work or school bag: PVC-backed 600D or PVC tarpaulin.
- Any market, everyday bag, rain not immersion: PU 1,000-2,000 mm.
- EU retail, cold climate, or eco claim: TPU, or PU with a C0 DWR face finish.
- Must be submersible: TPU with welded seams. Nothing else.
Test it before you cut it
Every coated roll we ship passes coating adhesion and hydrostatic head on the inspection frame; TPU and PVC lots also pass a cold-flex test at the target market's winter temperature. The six-gate bag QC process at the factory then checks seams on the finished sample - because a waterproof fabric with a leaking seam is still a wet bag.
Free colour card and swatches
Get the colour card and three fabric proposals for your bag
Tell us the bag type and target price. We reply with two or three fabric options, swatches by courier and, if you need the bags made, a sample plan from our sister factory.