Our premium sake drinkware series, Nousaku, is made of 100% tin. In Japan, pure tin is an auspicious metal as it is imperishable, rust-proof, and has been believed that water in a pure tin container does not spoil. 
The third most valuable metal after gold and silver, it has been believed that pure tin removes excessive bitterness from sake and produces better taste. The antibacterial and antioxidant properties of pure tin helps remove impurities, giving a round taste to the sake. 
Keep your Nousaku cup and pitcher in a refrigerator & you'll be surprised at how it retains the temperature of the sake over a meal.