1 pound density polystyrene is strong enough to support significant weight.
A common question we receive is "how much weight will polystyrene support?"
Polystyrene provides excellent strength and is commonly used underneath highways and in heavy construction. It will show visible dents, but can support the weight of a human without crushing or breaking. For added durability, there are numerous foam coatings ranging from concrete, Dryvit, plaster of paris, specialty foam coatings, latex paint, etc. that will create a hardened shell on your foam which can withstand many years of repeated use.
The foam in this listing is 1lb per cubic foot density.