Here's a helpful tip from November's issue of InStyle magazine: to perk up a saggy butt, make sure your jeans have at least 2% stretch, like Lycra (p. 199). This is according to Susie Crippen of J Brand jeans. She says, "Pants with more than 98% cotton can stretch out as soon as you wear them and give no support" (p. 199). I've personally found that more than 2% is too stretchy, but it's just a matter of how much give you want your jeans to have. Here are a couple pairs of J Brand jeans that have 2% stretch.