Eh, I don't know the name for them. My trainer had some out of package that she gave me because a gelding I had a few years back needed leg protection, but I wanted to wear wraps and not splint boots. They are like hard like a splint boot where the protection is needed, but then they are cotton-like to wrap underneath the polos.
Trust me, I was equally astonished about them. I haven't seen anything like them since Toni gave me my pair. She says they sell them at tack stores, but I have yet to find any. Best part: You can use them without the wraps, too, so if I don't want to put polos on I can just use those. Granted I don't have a horse who really needs protection anymore, its just safety.
I'll try to get some pics for you guys. These really are the best thing I've found in a long time