I've observed printing PETG that the primary if not the only reason for using a high bed temperature seems to be preventing the bed from acting as a huge heat sink and rapidly cooling the initial layers such that they don't bond well to each other. In particulat, the heat is not needed for adhesion-to-the-bed purposes. This got me thinking whether there's a way we could get rid of the requirement, as a way to save time and all the energy spent heating the bed and cooling the room it's eventually dumped into.
With that in mind, are there viable bed materials that are good thermal insulators? Just putting down a layer of any insulating material between the underlying bed and buildtak or whatever surface you want might work, but I would think these kinds of print surfaces are designed for moderate to high thermal conductivity themselves, and wouldn't be as bad a heat sink as the underlying metal, but might still sap a noticable amount of heat out of the part right away.