What are Recycled Shirts? Here's How it Works. Polyester is a petroleum based product that is fundamentally no different from plastic bottles. This makes polyester a synthetic fabric what can be bad for the environment. In order to combat the effect that polyester has on the environment we have adopted a new method for making the polyester fibre, recycling plastic bottles. Every Shirt in this collection uses between 1.8 and 7 recycled plastic bottles.