I use mine at room temp but the best way to change the temp if cold or hot water from the tap. Everyone will have different suggestions but those are mine. If you read reviews on glass there are ideas discussed on how to heat and cool your glass pieces.

DO NOT freeze,microwave or boil the toy though, freezing it can cause it to get stuck to your body parts like tongue frozen to pole OUCH. Microwaving and boiling the toy can get it way too hot cause you to burn yourself or your partner. Also using the boiling or microwave can heat your glass unevenly, meaning you will think the one part is perfectly fine when the other part won't be. Hope this helps.