PS plastic single wall jar with 70-400 neck finish. Single wall jars are normal 1-piece jars. They're called "single wall jars" to distinguish them from the 2-piece double wall jars. This jar is made of polystyrene (PS). PS is light-weight, hard, and has an almost glass-like appearance. It is shiny and classy. It has limited flexibility and is more brittle than other plastics. Essential oils may damage polystyrene, causing products to leak. Products with essential oil content will work better in PET or glass containers. This jar is typically used for lotion, cream, serum, gel, putty, clay, hair products, skin products, cleanser, and other personal care products. This jar has a 70-400 neck finish, and will fit closures with the same finish. The first number is the diameter of the container's opening (in mm). The second number refers to the thread/style/depth of the closure's skirt.