It's better to put the headlight on a piece of hardwood like birch when baking them in the oven. Any hardwood will do though. There is less risk of the plastic melting that way since it won't be touching any metal. Heat the oven to 200-250 degrees and bake for 5-10 mins. I have heard of people baking at 300-350 for only a few mins, but that seems a little hot for the headlight housings. I've done it dozens of times with my headlights.