The Herp Habitats are plastic. You just have to be careful with plastic and heat mats...there is one heat mat that Zoo Med makes that is specifically for plastic habitats...I believe it is the smallest one...the other heat mats would melt the plastic. A dome lamp is optional...I'm just saying that many garters do like to bask under the heat and light of a lamp. But you want to be careful not to have too much heat...a thermostat is the best way to ensure that you keep your temps where you want them on the warm and cool sides. If you are using the Herp Habitat or a small ten gallon tank...you probably wouldn't need a heat mat and a lamp...it might make it too warm. The caresheet will tell you the optimal temps that you are aiming for.