Polystyrene or styrofoam is made from petroleum, so it is very flammable and may not be safe to use as improvised wall insulation. It is illegal to burn styrofoam since this would release harmful chemicals, notably benzene to the atmosphere, which is a known human carcinogen used in the manufacturing process of polystyrene.
It is bulky and hard to recycle, and takes an incredible amount of time to break down. Polystyrene foam will be around highly long in the landfill. The use of polystyrene for food packaging is now banned in some US cities. Environmentalists and oceanographers also note that EPS is one of the main ocean pollutants, in an area in the northern Pacific Ocean that’s said to contain 3.3 million pieces of plastic garbage per square kilometer.
Styrofoam recycling is a cause for concern in the US because there are still few cities that have facilities to recycle this material and because of contamination issues in the EPS used in the food industry. The last one is a particularly costly issue– recylers have to spend more resources on personnel and work hours just to clean up the used food packaging material they collect before these can be recycled. Recently there are some advanced technologies that will allow recyclers to accept used food packaging for recycling, it will be more common to recycle polystyrene or styrofoam in the future.