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This will probably surprise you. Radiant Barrier has NO R-Value. R-Value is a term to describe how quickly heat will pass through or ...

What is the R-Value or R-Rating of Radiant Barrier Foil Insulation? This will probably surprise you. Radiant Barrier has NO R-Value? Yes, Radiant Barrier by itself has NO R-Value. Radiant Barrier can be attached to some products like Bubble Insulation, insulated sheathing, and radiant barrier decking like TechShield or Polar-Ply. The product will have have the r-value of the bubbles, sheathing or OSB decking, but the Reflective Foil does not actually provide any additional R-Value. So What is R-Value? R-Value is a term to describe how quickly heat will pass through or be absorbed by a product. This testing only applies to Conductive Heat Flow. Every product has a different R-Value. For example, wood has an R-Value of 1 for each inch of wood. So three inches of wood has an R-Value of 3. StyroFoam or EPS (expanded Polystyrene) has an R-Value of 3.85 per inch. So, three inches of Styrofoam will have an R-value of over 11. This is why we don't make coffee cups out of wood. Conductive heat will only pass through a solid object. Radiant heat is heat that passes through a gas or a vacuum. So, How does a Radiant Barrier Affect R-Value? Reflective Radiant Barriers reflect 97% of the radiant heat from hitting an object. By doing this, it makes the r-value of a material more effective. Here is an example: If you fill two ice chests with ice cold drinks and place one in the sun and the other in the shade which one will stay cold longer? They both have the SAME R-Value. But, by placing one ice chest in the shade you effectively put a radiant barrier over it and it did not have the opportunity to absorb any radiant heat. This is why we sit under an umbrella on a hot day rather than put on a heavy jacket to keep from getting hot. What about R-Value and Bubble Insulation? Yes, bubble foil has some R-Value. However, I see claims of as high as R-14 for some bubble products. If you read the fine print, this is always part of an "assembly" which usually includes a lot of "Dead Air Spaces" In a lab you might be able to create a perfecty tight seal on bubble foil, but in the real world it is virtually impossible. If you have air flow around an object the R-Value does not really matter. For example, if you have a heavy jacket and you unzip it and let air get between you and the jacket it does not matter how thick the jacket is because you have no dead air space. So unless you can completely air-seal the bubble foil you will not get the full effectiveness of the R-value. Bubble Insulation in Attics? You don't need the R-Value of Bubble Insulation if placed in a Ventilated Attic. All you need is a Foil Radiant Barrier. You will pay extra for the bubble foil, but will not get any additional benefit. Example: Would a 1 inch thick umbrella keep you any cooler on a hot sunny day? No. It would not since the Air Temperature is the SAME on either side of the umbrella. This is why we do not put insulation on INTERIOR Walls. R-Value only matters if there is a difference in temperatures on either side of the insulation. The same thing is true if you staple it to the bottom of your rafters and allow air to flow on both sides. Bubble foil is recommended for metal buildings to stop condensation and on the backside of kneewalls to stop "hotwalls". But stapling it to the bottom of your roof deck is overkill and you create the potential to trap moisture since bubble foil does not allow water vapor to pass through.

 

 

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