They're a cross btwn leggings and denim and anytime I leave the house lately I've been living in them. They are stretchy and soooo comfortable and I wear them tucked into my comfy boots and look remotely decent. As opposed to the sweatpants look- not attractive. I plan to spend the next 7 months in these and have a decently fashionable pregnancy!!
I bought my pair randomly at Filene's but I'm sure you can order them online. Just buy them a size larger than usual (so I got a L rather than M) and they fit really comfortably around the waist. I'm so happy these are around right as I'm pregnant!!