Some of these cladding or roofing units are expensive, especially the sandwich units which contain a middle layer of highly efficient thermal insulator, such as expanded polystyrene or glass fibre.

• 有些围护墙或屋顶构件造价很高，尤其是夹层式构件。这种构件中间有一层高效能的隔热层，如膨胀聚苯乙烯或玻璃纤维。