R10 rigid =/= R10 Fiberglass?

Old 10-15-15, 06:35 AM
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R10 rigid =/= R10 Fiberglass?

Just wondering if generally R-rating is uniform when looking at Fiberglass vs Rigid.
Old 10-15-15, 06:44 AM
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Not my area of expertise but I'm pretty sure R ratings are the same no matter which material is used although foam is less likely to allow air penetration.
Old 10-15-15, 07:38 AM
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The rigid insulation will absorb less moisture from the air so the R-value will degrade less over time. Rigid doesn't sustain flames but it will emit toxic smoke if a fire is nearby so it requires fire protection when installed in a living space.
Old 10-15-15, 08:52 AM
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In the testing lab they are similar, but in the real world the location they are used will result in different performances. Example, fiberglass insulation exposed on one side will be subject to air currents and lower its r-value.

Rigid foam has a better reputation simply because it eliminates much of the air flow and all of the air flow if well sealed. BUT, for cavity fill applications I do like mineral wool, (Roxul is one brand). It is very dense and doesn't have the chemical issues of rigid foam.


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