How does foam affect the environment?

Plastic (particularly packaging) is generally not recyclable or biodegradeable. This means that when you have used it you have no choice but to throw it away. If you use glass packaging for example the glass can be cleaned and reused (this is what happens with beer bottles etc). You can't do this with plastic. So lots of it gets thrown away. When you throw away, say, paper it degenerates into mush over time and disappears. Plastic doesn't do this so it means more and more space has to be given over to be used as dumps.

Because plastic isn't recycled (like glass can be) we need to make a lot of it: that requires the use of a lot of electricity so this is bad for the environment too.

Also it is made from petrol byproducts and obviously the process of extracting petrol from the earth is particularly environmentally unfriendly.