HomeGlossaryPolyurethane Coating (PU Coating)
Polyurethane Coating (PU Coating)
Treatment — one of 37 in the glossary
A thin layer of polyurethane applied to the inside face of a woven shell fabric to stop water passing through it. It is the cheapest way to make a jacket genuinely water-resistant, and the trade-off is breathability: a plain PU coating is a barrier in both directions, so moisture from the wearer has nowhere to go unless the coating is microporous or the garment is vented.
A barrier on the inside
The coating goes on the inner face, not the outer one. The outer face usually carries a separate durable water repellent finish that makes rain bead up; the PU layer is what stops anything that gets through from reaching the wearer.
It is measured as a hydrostatic head — the height of a column of water the fabric resists before leaking. A light shower jacket might be rated at 1,000 mm, serious rainwear much higher.
Thicker coatings resist more water and breathe less. That is the entire design trade-off.
Breathability and the microporous version
A solid PU film blocks water vapour as effectively as liquid water, so a cheap coated jacket gets clammy from the inside.
Microporous and hydrophilic coatings are engineered to let vapour through while blocking liquid. They cost more and they are what a spec sheet means when it claims a coated fabric is breathable.
Mechanical venting — pit zips, mesh-backed vents, a loose cut — is the other answer, and on cheaper garments it is the only one.
It ages, and it affects decoration
PU coatings hydrolyse: they absorb moisture over years and eventually break down, which is the flaking you sometimes find inside an old jacket. Storing a coated garment damp accelerates it.
For a decorator, the coating is on the inside, so screen printing on the outside is usually fine — but the heat of curing or pressing can damage the coating if it is too hot.
Embroidery perforates the barrier. Every needle hole is a potential leak, which is why decorated waterproof garments are normally embroidered only on panels where it does not matter, or printed instead.
Common questions
- What is a PU coating on a jacket?
- A thin layer of polyurethane on the inside of the shell fabric that stops water passing through. It is the most common and cheapest way to make a garment water-resistant.
- Does a PU coating make a jacket waterproof?
- Water-resistant to a rated degree, measured as hydrostatic head. Whether that counts as waterproof depends on the rating and on how the seams are finished.
- Why does my coated jacket feel clammy?
- Because a solid PU film blocks water vapour as well as liquid water. Breathable versions use microporous or hydrophilic coatings; cheaper garments rely on vents instead.
- Can you embroider on a PU-coated jacket?
- You can, but every needle hole punctures the waterproof barrier. Decorated waterproof garments are usually printed, or embroidered only where a leak does not matter.
See also
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