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**Published:** Jan 2002

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**Source: **STP1426-EB

The purpose of this presentation is to explain how specification tolerances re determined for thermal resistance in thermal insulation. Variation in measured test results is an important concept in the determination of specification tolerances. When a test of a product property is repeated, the measured test result isn't exactly the same as in the first test. This normal variation in measured test results is described by the normal robability frequency distribution curve, the bell-curve. A measure of this normal variation is the standard deviation. Specification tolerances are established from a table of probabilities of the normal curve by determining the position of the appropriate confidence level in terms of a constant multiplied by the standard deviation. A similar concept is involved in new ISO standards, in which a double confidence level is used.

**Keywords:**

building insulation, mineral fiber, thermal resistance, R-Value

**Author Information:**

Rushforth, RJ *Senior Research Engineer, ASQ Certified Quality Engineer, Johns Manville, Technical Center, Littleton, CO*

**Committee/Subcommittee:** C16.40

**DOI:** 10.1520/STP11003S