The cost savings can be significant. A pair of down pants will probably set you back $150 at REI; I made my Gore Tex shell, nylon-lined down pants for around twenty bucks (it helped that Wally World had Gore Tex in the dollar bin). A few years ago I ordered enough Power Dry from Malden Mills to make two sets of long underwear. If I remember right, I paid about twenty-five bucks for the material, whereas a set of Power Dry underwear usually sells for about sixty bucks.

But there are actually two main reasons I sew. First, I can make gear that fits perfectly and functions just the way I want it. No unnecessary bells and whistles, just good form and function. Second, I think it's kind of cool that almost all my hiking gear is home made. Maybe this is silly, but it fills me with a sense of pride that I'm actually out there surviving on gear I made myself.
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My blog on politics, the environment and the outdoors: Haiwee.blogspot.com