"Light, Affordable and Oh so Appealing" Since their introduction, Double wall jars have been extremely popular because their polypropylene inserts in a double wall construction allows a customer to get the high gloss finish of polystyrene on the outside without the typical compatibility issues inside. Our Double Wall jars are of the highest quality construction. Cosmetic in appearance, they come with both round and straight bases. We stock all double wall jars in white and offer both polypropylene inners with polypropylene outers and polypropylene inners with polystyrene outers.