the jagers have specially treated glass to prevent that happening, if you search youtube you may also find a rena being run over by a van. i would be more concerned by how they actually heat & maintain the temp of the tank, that to me is what makes a good heater & not if you can fully heat them up & drop them into a tank or be able to run over one. i personally recommend jagers for the fact they do a better job as a heater than others i have had.