What material is in laptop backpacks?

What material do you call that protective foam padding in the laptop sleeve section of backpacks? I bet there is several types depending on the bag, but what is the exact name? Is it Closed-cell Foam? etc?

I'm trying to find a place that sells it in bulk. A link(s) for that would be AWESOME!!

Any advice helps and is appreciated. THANKS!! :)
 
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