What are those extra thick hang tags you find on some clothing made of?

I'm trying to find something a lot thicker than 14-16pt card stock to print some hang tags for a clothing company. If anyone has specific links to sites that offer printing on fairly thick materials, or even knows what those materials are, it would be greatly appreciated. I'm talking primarily about streetwear companies like LRG, Crooks and Castles, Know1edge and Lira that have these awesome durable, thick tags, that almost feel like a cross between cardboard and plastic. thanks!