Looks like Tin, but it is Stainless Steel, satin finish:  Will not corrode and easily cleaned.

The Boiler holds 24 oz. with a top that is attached, a handle and metal loop to hang by the fire.  You can make your morning coffee, or soup for lunch.  Take it with you around camp for a drinking vessel.  It is one of the best additions to your camp gear.

Once it has been by the fire it looks like the tin versions but does not corrode if you forget to clean it right away.