What's the most green container for a cup of coffee? According to Slate's Green Lantern column, the answer is not as simple as you might expect.
Polystrene, even though its made from petroleum, has the advantage of being extremely light weight. Therefore, it takes less energy to manufacture and transport compared to paper or ceramic. The amount of water and energy required to wash the ceramic cup using a dishwasher, according to the 1991 study mentioned in Slate's explanation, approximately equals the energy required to manufacture a new polystyrene cup. Note: washing by hand can actually use more water and energy than a dishwasher!
Still, that doesn't get around the problem of solid waste, and this is where the ceramic cup wins. So the greenest cup, it turns out, is the one that you already own.
image by adevv via sxc.hu