Useful product as it is airtight with a screw-on top which itself has an upper screw top compartment supposedly for a tea bag or something but the lower part can leak a little into it from a type of pressure vent/airhole . Keeps drinks hot for ages. Can keep stuff cool as well. Pity it isn't dishwasher safe. The coating on the black version will come off if you put it in the dishwasher (oops!) but it has a pleasant slightly non-slip texture whereas the steel version is more slippery to hold. Good size for car cup holders. Makes a good present for a practical person! Useful at home as well, just to keep your drinks warm. Noticed my silver one had a 10 year guarantee, not 15.