Windstopper is a fabric made by Gore, the manufacturers of Gore-Tex waterproof fabric.
And it is made from essentially the same basic thing as the waterproof Gore-Tex fabric without one key component – the PU layer that is bonded to the PTFE membrane. And it tends to be used with less water-resistant outer fabrics (hard shells), and more with softer shells that don’t have taped seams.
The Windstopper membrane itself is a very fragile, very complex mesh structure which is made from a material called PTFE. This is closely related to the non-stick coating on your frying pan, and that stretchy white tape which plumbers use to seal joints. The process for creating the super-fine web was discovered when a massive stretching force was applied to a bit of solid PTFE very quickly. It stretched to around 8 times its original length and created a structure with tiny little blobs of material connected by strands.
HOWEVER, the Windstopper membrane is really fragile, and must be protected from your clumsy oafishness by encapsulating it between layers of protective fabric which also have nice big holes in them for vapour to pass through. On the inside, against your skin, that will be a soft or smooth face-fabric. And on the outside it will be a tougher, abrasion proof fabric. This outer face may be chemically treated with something called Durable Waterproof Repellent (DWR) to make rain bead-up and run off it. After all, if the garment is covered in rain, it can’t breathe to let your sweat out.
This is why Windstopper garments need to be kept clean and re-treated with DWR after a while. Read our guide on that here.
Gore-Tex is a Trademark of W.L.Gore and Associates.