What did Sir James Dewar invent?

Scottish physicist and chemist Sir James Dewar invented the Dewar flask, better known as the thermos, in 1892. The thermos is a container that minimizes the change in temperature within the flask, thus allowing cold substances inside to remain cold and hot substances to stay hot.

Dewar's invention was not intended for commercial use, but to help in his scientific work with liquid gases. The container was made with one flask inside another with a vacuum separating the two to minimize heat transfer. Several years later, two Germans used Dewar's prototype to make a commercial thermos, which they named from the Greek word "therme," which means "hot."