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David Hanson Posted: Sep 16, 2007 08:46 AM	Initial K-factor question If the manufacturer cites the "Initial K-factor" as 0.155 - 0.170 How does this relate to the aged R-value?
mason Posted: Sep 17, 2007 09:04 AM	A k factor of .155 is an R value of 6.45 and .177 k factor is 5.6. R value is the inverse of K factor. But that doesn't tell you the aged R value. The foam supplier needs to provide you with results from R value testing of an aged foam sample. Most of the 2lb and 3lb density closed cell foams (including extruded polystyrene, polyisocyanurate and polyurethane foams use blowing agents that provide greater R values than water blown systems such as 1/2 lb open cell sprayfoam and expanded polystyrene foam. However, over time, the intitial R value of XPS, polyiso and polyurethane foam can diminish when outside air is allowed to enter the foam cell walls. Most of this R value reduction takes place in the first 6 months. Therefore the FTC requires aged R values to be provided in advertising and material data sheets. Typically this R value reduction is around 5-10% of the intitial R value and approximately 90% of this R value reduction occurs in the first 6 months after application. This is why both the ASTM standard for spray polyurethane foam (C 1029) and the FTC reguire 6 month aging of samples before R value is measured. There are factors that can help minimize the R value loss in sprayfoam and other foam plastics. The thicker the installed foam the higher the aged R value, low perm rated substrates and coatings also inhibit the loss of R value. For example, field studies performed by the Navy in the 80s and 90s demonstrated that the 10 year old sprayfoam could have R values varying between 5.6 per inch to 7.2 per inch depending on the type of substrate, thickness of foam and type of covering. (metal surfaces, and butyl rubber, some polyurethanes and polyurea coatings have low perm ratings and minimize R value loss of sprayfoam. The foam manufacturer you reference should have aged R values listed including the test procedure that obtained the value.

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Comments

David Hanson

Posted: Sep 16, 2007 08:46 AM

Initial K-factor question

If the manufacturer cites the "Initial K-factor" as 0.155 - 0.170 How does this relate to the aged R-value?

mason

Posted: Sep 17, 2007 09:04 AM

A k factor of .155 is an R value of 6.45 and .177 k factor is 5.6. R value is the inverse of K factor. But that doesn't tell you the aged R value. The foam supplier needs to provide you with results from R value testing of an aged foam sample.

Most of the 2lb and 3lb density closed cell foams (including extruded polystyrene, polyisocyanurate and polyurethane foams use blowing agents that provide greater R values than water blown systems such as 1/2 lb open cell sprayfoam and expanded polystyrene foam.

However, over time, the intitial R value of XPS, polyiso and polyurethane foam can diminish when outside air is allowed to enter the foam cell walls. Most of this R value reduction takes place in the first 6 months. Therefore the FTC requires aged R values to be provided in advertising and material data sheets.

Typically this R value reduction is around 5-10% of the intitial R value and approximately 90% of this R value reduction occurs in the first 6 months after application. This is why both the ASTM standard for spray polyurethane foam (C 1029) and the FTC reguire 6 month aging of samples before R value is measured.

There are factors that can help minimize the R value loss in sprayfoam and other foam plastics. The thicker the installed foam the higher the aged R value, low perm rated substrates and coatings also inhibit the loss of R value.

For example, field studies performed by the Navy in the 80s and 90s demonstrated that the 10 year old sprayfoam could have R values varying between 5.6 per inch to 7.2 per inch depending on the type of substrate, thickness of foam and type of covering. (metal surfaces, and butyl rubber, some polyurethanes and polyurea coatings have low perm ratings and minimize R value loss of sprayfoam.

The foam manufacturer you reference should have aged R values listed including the test procedure that obtained the value.

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