Waterproof membranes (ePTFE / PU)
A thin film laminated to the shell fabric that blocks liquid water but lets water vapour escape. ePTFE (expanded PTFE, the classic Gore-Tex type) and PU are the two main families.
How it’s made
- 1ePTFE: PTFE is stretched into a microporous film whose pores are too small for droplets but pass vapour. Usually paired with a PU layer.
- 2PU: a solid hydrophilic or microporous polyurethane film moves vapour by diffusion.
- 3The membrane is laminated as 2-layer, 2.5-layer or 3-layer and finished with DWR. Seams are taped.
What to look for
- PFC-free membranes and DWR. Several brands have moved to ePE or PU.
- 3-layer for durability, 2.5-layer for lightweight running shells
- Fully taped seams
Pros
- Truly waterproof
- Windproof
Cons
- Less breathable than a wind shell during hard running
- PTFE is a fluoropolymer and part of the PFAS debate
- Hard to recycle
Typical use
- Running:
- Rain jackets for wet and cold races.
- Streetwear:
- Technical outerwear.
Sustainability
Look for PFC-free options and repairability. The longer the jacket lasts, the lower the impact per use.