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[herptrader]

YES!

If you don't use a thermostat well insulated pockets can cause overheating and can lead to dissaster.

When I was at the VHS reptile expo a woman came up to me and asked if it was normal for heat mats to discolor where they were under the click clack. It seems that the pocket of air under the plastic was trapping sufficient heat to discolor the plastic. It is also important to position the probe of the thermostat close to where the heat mat will be at its hottest.

In a perfectly insulated setup even milliwatts will eventually cause heat build up.