Styrene is a liquid used to make polystyrene. Great for your chicken breasts – not so good for your pictures. Styrene is used for lower priced frames because it is far cheaper than acrylic.
As you will see below, 2 mm cast acrylic supports your picture far more. It is also hard to break. It is clearer than glass and protects against fading caused by the UV (ultra violet) in light.
This is why we only use cast acrylic.