The offered Double Wall Jar are made of plastic and is a high quality packaging option mainly used in the cosmetic industry. It has a glossy finish throughout and itâs wide mouth design makes it ideal for personal care cream or powder products. What makes the double wall jar unique is its two-layer construction â think of it as a jar within a jar. The jars are made of plastic and are a high quality packaging option mainly used in the cosmetic industry. The double wall gives the product a more professional look than the single wall jars. Double Wall Jar is very effective.