Looks like an ordinary waistband on some summery pajama pants. But look closer - see how it's stretched out completely?
This is a case where marinating in stash is not a good thing. When I sewed up these pajama pants just before Easter, I dug around in my stash of elastic, and came up with a hank that had obviously been there a while. It went in fine. the pants were great. I took them to the cottage for Easter, and the first night, when I put them on, I thought, hmmm, they're a touch looser than I usually make them. Considering the amount of chocolate I'd been testing, (Can't give the kid untested chocolate, now could we??), I didn't think I'd lost and inch or more around the waist. Whatever, it was late, I was tired, I went to bed. The next morning when I got up, I realized it was not my waist. These pants were falling right off me! The elastic I used has lost all elasticity! My husband thought it was pretty funny, seeing me hitch these babies up all the time!
Luckily, it's an easy fix - new elastic, and they're as good as new. Which is good, becasue this cotton seersucker is incredibly comfortable.
The downside - getting rid of a ton of old hanks of elastic that's no good any more. Good think wool doesn't lose any thing with age...