Heat tape. Is a thick plastic film that has 2 metal strips (one on each side ) and connections going back and forth. When electricity is applied it heats up. Hence why u always want to regulate it with a dimmer (limits the amount of electricity going thru hence less heat) or with a thermostat (on/off) that will only let it get to a certain temp and then stop all electricity or a proportional thermostat which essentially self regulates the amount going to it , in essence am automatic dimmer switch.How does heat tape work exactly? That's something that's been confusing me for a while. I don't plan on making a rack anytime soon but I think knowing this beforehand is a very good idea.