The top-rated heating, venting and air conditioning duct insulation type is fiberglass insulation with a metallic backing, often referred to by its insulation or R value. Insulation composed of polyethylene bubbles sandwiched between reflective layers is useful in some applications but is usually less effective than traditional fiberglass duct insulation.
So-called "bubble wrap" insulation is often less expensive than traditional insulation, and manufacturers often claim it is as efficient at insulating ducts as fiberglass. However, the effectiveness of bubble insulation often depends on the presence of a considerable amount of airspace around the duct in question. However, bubble wrap insulation may outperform fiberglass in warmer climates or in situations where condensation or mold are concerns.