Polyethylene is the most common plastic in the world. It is a super versatile polymer (molecule from repeated subunits) and when it comes to cosmetics, it is often referred to as microbeads. Well, it used to be referred to as microbeads, as it was banned in 2015 in the " Microbead-Free Waters Act" due to the small plastic spheres accumulating in the waters and looking like food to fish. Well done by Obama.
But being versatile means that polyethylene does not only come as scrub particles but also as a white wax. In its wax-form, it is still well, alive and pretty popular. It thickens up water-free formulas, increases hardness and raises the melting point of emulsions and water-less balms. It is particularly common in cleansing balms and stick-type makeup products due to its ability to add body, hardness and slip to these formulas.