Styrene Acrylonitrile (SAN)

AS, more commonly called SAN, is a copolymer of styrene and acrylonitrile. The acrylonitrile content gives a step up in chemical resistance and heat resistance over straight polystyrene while retaining the clarity and rigidity that make PS attractive.

It is the usual specification when a brief calls for a clear, rigid cosmetic jar and the formula contains oils that would attack PS.

• Clarity and rigidity: Comparable to polystyrene.
• Chemical and oil resistance: Materially better than PS. Handles oil-bearing creams and most cosmetic actives.
• Heat resistance: Better than PS, up to roughly 85°C.
• Toughness: Below PETG and acrylic. An improvement on PS, not a tough resin in absolute terms.
• Cost: Above PS, below acrylic.

Cosmetic jars for oil-bearing creams and balms. Airless bottle outer shells. Compact cases and premium closure overcaps where clarity is required and the contents are not alcohol-based.

Process: Injection molding.

Shrinkage: 0.3-0.7%.

Drying required. SAN is hygroscopic. Undried resin produces splay and silver streaking that is immediately visible on a clear cosmetic part and cannot be polished out.

Watch for: Weld lines in clear parts. On a transparent jar a weld line is a visible defect, not only a strength concern, so gate placement has to be planned around sightlines.