If you can find any the E type foam it is about twice as efficient. But I would look around construction sites for scrap foam of any kind first. Even glass batting would work with the landscape fabric over it. Spray foam would be really nice but expensive unless you could haul it to somewhere where they were doing a job and had leftover foam they needed to get rid of.

"When you disarm the people, you commence to offend them and show that you distrust them either through cowardice or lack of confidence, and both of these opinions generate hatred." Niccolo Machiavelli