Polyester is extremely common in mattresses, in fact, almost all mattresses will carry at least some amount of polyester as it will often be used to create a micro-barrier between the top layer and the base layer. Regardless though, what is polyester? Well polyester is simply a synthetic resin that gets spun and used as wadding and fibre fillings. Polyester when used within mattresses is generally described as non-woven and thermally bonded material of polyester fibres to form a mattress sized pad of varying densities and weights. You will typically find polyester in mattresses from low-medium pricing scales, should you start going into very high priced mattresses, you can expect polyester to be replaced with natural fibre.