What aaron said then i what you want^ IMO paper based substrate would be your best bet. But the bark substrate could work fine too. You just have to get the depth of the layer right. I use switched from newspaper to sani chips recently and really like the look of them better. As far as heat i have not noticed a difference. If the snake is feeling cold then theyll just push all the substrate out of the way anyways. The hotspot is still 88 degrees no matter what haha