The J028 is a 1/2 oz frosted PP/PS plastic double wall round base jar with 48-400 neck finish. Double wall jars are 2-piece containers: the shell and the liner. It is called "double wall" because the two containers nested inside of each other create two walls. This jar has a rounded base. This jar is made of two pieces. The inside is made of polypropylene (PP). PP is light-weight, durable, flexible, and highly resistant to fatigue and heat. It has a high shatter-resistance rating. The outer piece is made of polystyrene (PS). PS is light-weight and hard. It has limited flexibility and is more brittle than other plastics. This is a great container for products containing essential oils, so long as the ratio of oil to product is low (around 5% or less). 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 48-400 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.