Insulating the bottom will only be of use if the top and sides are already well insulated. A well designed entrance that allows plenty of air but keeps the heat in, then follow that with an insulated bottom of the hive. An air filled cavity with a heat source and external heat lossing sets up convection currents. These convection currents circulate around the cavity, thus making the insulation of the bottom of the cavity a factor in the overall heat loss. Simple physics until the bees step in an alter things, like blocking the entrance, restricting airflow... :)
finski: v interesting ... how much insulation on the floor? at present I have ~ 50mm PIR = 75mm polystyrene