Closed cell is described as foam with a density of 1.5-2 lbs. or more per square foot.  This formula typically has a thicker resin and less rise time.   This makes for cell structure that has more rigid wall that form completely.

There are approx. 1 million cells per square in. in the closed cell foam.  Because of the complete cell structure, most formulas of closed cell are water proof insulation.  It is also puncture resistant.  An object must penetrate 100% of all cells and go COMPLETELY through the foam to form leaks.  If the
object penetrates 95% of the foam the system will not leak.  Because of the rigid cell structure this is perfect foam for roofing.

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