I think they are intended to be stuck to the underside on the outside and could therefore be pulled off and relocated (even if with great difficulty). If you have an exoterra type terrarium where there is a gap between the base and the support area it would be OK but it would be a problem on an aquarium type terrarium because the base would nor be supported properly and the heat would be trapped and may cause the base to brake because of differential expansion. That is one of the reasons why I don't use heat pads.