PU coating at a glance
- Fails by
- Hydrolysis
- Accelerated by
- Damp storage and heat
- Advantage
- Takes factory seam tape
Why manufacturers use it
Two practical reasons. Polyurethane bonds to seam tape, so a PU shelter can be factory sealed on the production line rather than sold with a tube of sealant and an instruction sheet. And it is cheap, which is why it dominates the budget end of the tent market.
It also builds hydrostatic head easily. A heavier PU layer raises the rating a fabric will hold, which is how a 3,000 mm floor gets specified without expensive materials. That is real waterproofing, at the cost of weight and stiffness.
Hydrolysis, and what it looks like
Polyurethane reacts with water over time in a process called hydrolysis, and heat and humidity accelerate it. The coating eventually becomes tacky, then flakes away from the fabric, and the classic presentation is a tent packed damp and stored in a hot garage that comes out smelling of vinyl with its floor peeling.
It is age and storage rather than use that drives it, which is why a lightly used ten-year-old tent can be in worse shape than a heavily used five-year-old one. Storing a shelter dry, loose and cool is most of the fix.
What this means when you're choosing
- Whether seams arrive factory taped, which is the practical advantage of PU
- Silicone or a laminate instead if you want the coating to outlast the fabric
- Storage advice, since hydrolysis is driven by damp storage more than by use
The common mistake
Storing it packed and damp
Hydrolysis is what kills PU coatings, and packing a shelter wet into a stuff sack in a warm space is the fastest way to cause it. Dry it fully, store it loosely rather than compressed, and keep it somewhere cool. Most tents that die of a flaking floor were killed in a garage rather than on a trip.
Common questions
Why is my tent floor sticky and flaking?
The polyurethane coating has hydrolysed. It is driven by damp storage and heat rather than by use, and it is not repairable in any lasting way, though a recoat product buys a season or two.
Is PU or silicone better?
Silicone lasts far longer and is lighter for the same strength. PU is cheaper and takes factory seam tape, which is why budget shelters arrive sealed and silnylon ones often do not.
Where this is defined
- ISO 811 hydrostatic pressure test for fabrics, International Organization for Standardization