Any synthetic which is a polymer of propylene.

Polypropylene, or polypro as the goofy yuppy hikers like to sling it around, is often used in technical clothing for backpackers, climbers, bikers, etc., because of its many useful qualities: it's very warm, it floats, it dries incredibly quickly, and for a synthetic, it wicks very well. (IE, beats the pants out of polyester, but sucks compared to cotton. Many of the more expensive "polar fleece" jackets are made with polypro; they are warmer and better in inclement weather than their cotton or cotton-poly lookalikes. While very trendy (a good barometer of how geeky a backpacker is is to ask them if they have cotton or polypro underwear), and undeniably useful (polypropylene socks are wonderful for skiing and cost as much as lunch for a week), for most people who don't sleep in the snow or spend the night on mountaintops polypropylene clothing doesn't offer much advantage over the much cheaper alternative of layered non-cotton clothing and a good stout rain jacket.

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