It is 2-inch-thick foam. This item was a gift for Christmas in 2008 and the product did not make it through the year. It does get you motivated to get out the door with your field guide. I cant tell a difference when the cover is on the bike and when it isnt. Now I have to try and find something else that will hopefully work before birth. _____*Cons:-Not compatible with our three mountain bikes with wide and flat top tubes due to poor cradle design. Everything else will be saved for my Halloween costume next year. I loved them they were perfect fit and very comfortable I use headphones constantly to watch TV and usually wear on-ear headphones but they become uncomfortable over time. The sound is great and the mic works well.