I see multiple references to polypro (aka polypropylene, olefin, polyethylene) on this thread. The original (e.g., Lifa) synthetic base layers were polypro. But that's old school stuff.
Capilene and most, if not all, current base layers are made of polyester. The old polypro stuff (e.g. 1975 Lifa) stank. Capilene and the other current polyester base layers are an enormous improvement re ...