Castelli nailed it with these seamless leg, knee and arm warmers. They must use a very high loft insulating fiber to knit them. They are super soft, stretchy and very warm for their weight and thickness. Although they look small when you get them, they stretch a lot. And thus far have not lost their shape or rolled down.
I expected these to have a fleece lining. Nope. Super thin but they were surprisingly adequate on a 45 day. Alright, okay! Then got a run in them. Once I took them on a longer ride I noticed they slipped down. Overall disappointment. But they will now be my go-to under tights on super cold days.
These knee warmers are comfortable, easy to get on/off, and plenty warm for me, but they won't stay up. If you get them, plan on stopping every hour or so to pull them back up into your shorts. I have since bought a pair of the Pearl Izumi Elite Thermal Knee Warmers, and they are much better. I am sorry I don't have two pairs of those.