They are a cross between a tight and a pant. Snug at the hips and buns, then looser (but not LOOSE) at the thighs and legs. It's the snugness that makes the butt look smaller and gives it a certain perky quality.

And I do think it's the tailoring, and not my butt shrinking. I look just as flabby-cheeked as always in my Levis today. Darn.

The fabric isn't swishy or slippery. It's a very soft brushed knit, kind of like a cotton t-shirt but much cozier. Or like an Ibex wool t-shirt. Yeah, I guess the closest comparison I can make is that the fabric is like an Ibex mid-weight shirt or boxer.