If a thing is heatproof, heat cannot damage it. You meet this word on kitchens and labels: a heatproof dish can go in a hot oven; a heatproof glove lets you hold a tray; a heatproof mat sits under a pan. Ordinary plastic is usually not heatproof — it can melt or bend out of shape. Special glass and some special plastics can be. People also say heat-resistant, which is close; though actually, heatproof sounds a little stronger, as if the heat cannot hurt the thing at all, while heat-resistant only claims it can stand a lot of heat. You may also see heat-proof with a hyphen. As a verb, to heatproof something is to treat or cover it so heat will not spoil it, but that use is less common than the adjective.