The air gap formed by the two layers of polycarbonate sandwiched together creates effective insulation properties, helping to keep plants warm in the winter, cool in the summer. Glazing on all sides & top allows for excellent light transmission, helping to prevent plants becoming 'drawn' or 'leggy'. Framework - sturdy structure created using 16 gauge maintenance-free, lightweight aluminium bolted together with aluminium round head bolts and nuts. The cleverly designed shape means the sloping lids on both sides not only create an excellent sun trap throughout the year but also allow maximum use of the space provided. Smaller or younger plants can be placed near the 8" high front and back edges, whilst larger specimens up to 2' high can be grown in the centre of the frame. Flexible Shelving - supplied with two shelves (one fitting either side). Fitting in the middle of the frame, 8" (20cm) from the top, the 6" (15cm) wide by 48" (122cm) long aluminium shelves provide extra space for seed trays & pots. Ventilation & Access - aluminium locking brackets with two opening positions enables the frame to be left securely open for excellent ventilation. Lower position allows air in whilst providing good protection from the elements; the top position is for maximum ventilation. Top panels can be fully opened to allow plants to be easily lifted in or out of the frame & allow easy watering.