Advertised as stainless and plastic. I ordered online thinking the stainless would be on the inside. Well, the stainless steel is on the outside and the inside where your coffee sits is in plastic! Not for me, I don’t like drinking coffee out of anything plastic. Looks good, and I like the grip material around the outside. I may use this for cold drinks. Plus, it says 12 oz. but instructions say only to fill 10 oz.