What's R-value?
R-Value is a measure of how well an insulation product resists the flow of heat or cold through it. R-value is determined by a laboratory test in which an insulation material is sandwiched between a cool and a warm surface.The ability of the material to resist temperature changes results in an R-value for that material.

So what's wrong with that?
A machine in a laboratory gives a relative number that can be used to compare products, but a laboratory R-value does not tell everything you need to know about the effectiveness of those products. Insulation is subjected to a wide range of temperature conditions in a house. The insulation is affected by air movement, and it is also degraded by the convection forces that develop within the insulation material.

Convective Loops
A convective loop, whether inside a wall cavity or in another part of the building structure, occurs when air rises along a warm surface and falls along a cold surface, creating a circular movement of warm and cold air.

A convective loop transfers heat through the building assembly, requiring more energy to replace the lost heat in heating seasons and the lost cool air in cooling seasons.

Improper installation of conventional insulation, light density blown-in insulation and structural items such as a drop soffit in the kitchen can create a convective loop.

Comparing R-Values for 2 x 4 and 2 x 6 Wall Construction

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