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In 1985, the ASTM Task Force on ASTM Test Methods for Water Vapor Transmission of Materials (E 96-80) initiated a round robin with two objectives: 1. to prepare a new precision and bias statement for use in ASTM E 96-80, and 2. to evaluate possible new water vapor transmission standard materials to be inventoried by the National Bureau of Standards.
Three plastic films (1-mil Mylar, 5.5-mil Teflon FEP (fluorinated ethylene propylene), and 5.5-mil high-density polyethylene, HDPE) were chosen for inclusion in the round robin. The Mylar film was intended to be the high water vapor transmission standard, and the other two films were the candidates for a possible low water vapor transmission standard.
Twelve laboratories participated in the round robin that requested that each laboratory test all three films in triplicate using ASTM E 96-80 Procedures A and B (desiccant and water method) at 23°C (73.4°F).
Some of the twelve laboratories obtained results with a wide disparity, especially on the low water vapor transmitting films—Teflon and HDPE. Other laboratories obtained precise results. The wide variance in some laboratories' results was judged to be due to those laboratories not sealing the test samples thoroughly.
Results from the round robin are discussed and have led to the following actions: 1. a second round robin is planned, 2. 12.7-mm (1/2-in.) thick foams will be added to the round robin so that the precision and bias statement can be more complete, and 3. the HDPE film has been eliminated as a candidate material.
water vapor transmission, water vapor transmittance, permeance, standards, reference material, testing
Senior Product Development Engineer, CertainTeed Corporation, Blue Bell, PA