Good insulation helps to retain the solar energy absorbed by thermal mass materials. Keeping heat in requires you to insulate all areas of the greenhouse that are not glazed or used for heat absorption. Seal doors and vents with weather stripping. Install glazing snugly within casements. Polyurethane foams, polystyrene foams, and fiberglass are all good insulating materials. But these materials need to be kept dry to function effectively. A vapor barrier of heavy-duty polyethylene film placed between the greenhouse walls and the insulation will keep your greenhouse well insulated
On aquaponics greenhouse floors, brick, masonry, or flagstone serves as a good heat sink. However, they can quickly lose heat to the ground if there is not an insulating barrier between the flooring and the soil. To protect against heat loss, insulate footings and the foundation with 1- to 2-inch sheets of rigid insulation or with a 4-inch-wide trench filled with pumice stone that extends to the bottom of the footings. You also can insulate flooring with four inches of pumice rock. Besides insulating the floor, this method also allows water to drain through.
This information is courtesy of ATTRA - National Sustainable Agriculture Information Service