The Stacking Mug Set M is made of ultralight Japanese titanium using a historic manufacturing process. The Stacking Mug Set M is designed to be multi-use, the smallest mug is perfect for drinking and the largest is ideal for holding food. Each mug is made of double-walled titanium and can nest within each other for simple storage. Please note: double-walled titanium cannot be placed over an open flame or heat source. Pair the Stacking Mug Set M with the Titanium Spork or Titanium Flask.