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The blue stuff is the more expensive "closed-cell".
Very hard to the touch, but not bondo-hard. I was told they insulate airliners and industrial structural items with it. Much like thick soft plastic. 3M is getting into that game, and the "R-value" standards will be changed to "air exchange".
The yellow stuff is the cheaper "open cell".
Relatively soft, and quazi-breathable in terms of moisture exchange(over a long period of time).
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