Plant life is very specific to temperature, and when horticulturists grow during the cold seasons they demonstrate specific attention to the insulation of their grow cabinets. Cooler temperatures can reduce plant growth drastically, or even kill the plant. This is why much attention is necessary when designing a grow cabinet. Thankfully, once these precautions are taken, growing plants in the cabinet is much easier than it would be if the cold were accounted for later in the grow cycle. Insulating a cabinet is inexpensive, takes little time, and ensures the health of your plants.
Drill a 3-inch hole on the left wall and the bottom left side, and drill another hole on the right wall, top left side. These will be air flow holes.
Measure the walls, ceiling, and floor in your cabinet to cut your foam insulation accordingly. If you make all the measurements first, accommodate for the 1/2-inch thickness of the insulation. Cut the insulation flush with the door so there is a place for it to fit snugly when the door is closed, and attach it to the door with the Velcro adhesive 3 inches from the outside edge.
Measure out the Mylar by taking the measurements from the foam insulation, and add 2 inches to both length and width. Tape the Mylar to the wall and cover the seams with the metal tape. Fold the Mylar over the foam on the door and tape to the insulation to the foam.
Cut out the foam and Mylar that covers the holes you drilled with the box cutter.
Cut the net screens to cover the holes, and tape them with the metal tape. When attaching your hardware in this cabinet, you want duct work that fits over this holes. This way, a fan can circulate air effectively.