Insulated box inside with expanded soy bean foam. The bottom insulation keeps the growing medium warm and has plenty of depth for good root growth. Sytem is drained by tubes placed to assure a reservior of moisture. Salad Box 24" x 18", insulated, (1)-24" grow light, hard cover.This may look like an old fashion cold frame – but it really is a HOT box or hot frame. The interior is insulated with soy-based foam – bottom and sides. The heat comes from a 24” (or in the BIG box a 48”) fluorescent, double bulb, grow bulbs/lamps. Heated with heat lamps. We have tested these salad boxes since 2000. The MiKris Eco Salad Box™ on a January day when the temperature was -12F and there was eight inches of snow on the ground still did well. You can see them at www.mikriscoop.com.