I thought I would try to make a listing which people could add to of the best warranties that people have found from the actual companies. Where you can just send a product back and it is replaced with the same or similar if it fails or does not measure up even 5 years later. Still looking for the magical underwear warranty.
Darn Tough: socks
Outdoor Research: handwear, headwear, rainwear
Backcountry (Stoic): full line including wool
REI: full line

