Popular Exterior Wall Insulation Products Tested for Absorption and Drying; Polyiso Performs Better when Compared Head-to-Head with Mineral Wool Wall CI
ATLANTA – October 12, 2020 – Atlas announces the results of a scientific research study that compared two common exterior wall insulation products – polyiso and mineral wool wall CI and how each performed when subjected to wetting. The research study1, conducted by M. Steven Doggett, PH.D., a principal scientist of Built Environments, Inc., showed strongly favorable results for polyiso, which is important as new practices in wall design advance. The testing proves that when polyiso is compared to mineral wool wall CI using the same test methods (ASTM C209), mineral wool wall CI absorbed 8 to 38 times more water than foil-faced polyiso and took an additional two to six days longer to dry than polyiso. These head to head results provide a better understanding of how these two continuous insulations handle bulk water, and should be taken into consideration when managing water and moisture in the building envelope.
“With design practices favoring the use of exterior continuous insulation, it’s important for architects and engineers to understand how the most common insulation solutions perform under identical circumstances – specifically when exposed to liquid water, not just water vapor, since the exterior layer is more prone to water exposure,” said Tom Robertson, Business Unit Manager for wall insulation at Atlas Roofing Corporation. “Materials considered “open pore”, like mineral wool wall CI, are more susceptible to greater water absorption than “closed pore” insulation like polyisocyanurate (polyiso).”
Findings Now Defy Common Claims Regarding Absorption and Drying Behaviors
Mineral wool wall CI and polyiso, while both used as exterior continuous insulation (CI) in the building envelope, are tested to different water absorption test methods. When referencing published manufacturer’s literature there is no accurate comparison of their performance characteristics in regard to absorption, rewetting and drying. Mineral wool wall CI has typically been tested in accordance with ASTM C1104, which utilizes water vapor (95 ± 3% RH). Polyiso, on the other hand, is tested in accordance with ASTM C209, which submerges the product under one inch of standing water for two hours. However, when mineral wool wall CI and polyiso are both tested to ASTM C209 testing protocol, the results are clear that polyiso performs better. Mineral wool wall CI absorbed up to 78% of its weight in water, while polyiso absorbed less than 4% of its weight in water. Drying times for mineral wool wall CI ranged from three to seven days, while polyiso was dry in 24 hours.
Mineral Wool Wall CI vs. Polyiso Insulation: The Results
The behaviors of mineral wool wall CI and polyiso were assessed by standard two-hour water immersion. In addition to mineral wool wall CI absorbing eight to 38 times more water than polyiso, it was found that mineral wool wall CI also required two to six days longer to dry. A lack of sorption2 consistency within mineral wool wall CI products creates a wider variation in drying times, which is why tests show a range of three to seven days to achieve the same endpoint of .05% water content. Additional findings showed:
- Mineral wool wall CI absorbs 18% to 78% of its weight in water. In comparison to polyiso, mineral wool wall CI absorbs 8–38 times more water than foil faced polyiso and 4–19 times more water than coated glass faced polyiso. These findings prove water absorption is directly linked to pore structure. Open, fibrous mineral wool wall CI absorbs and retains significantly more water than rigid, closed-cell polyiso.
- Mineral wool wall CI is inconsistent. Tests were conducted on two different brands of mineral wool wall CI with similar product declarations, but significant differences in absorption rates were observed. Sorption values even varied significantly between individual pieces from the same product bundle for each manufacturer.
- Polyiso samples vastly outperformed mineral wool wall CI. Foil faced polyiso absorbed 2% water by weight, or 0.065% by volume, while coated glass faced polyiso absorbed less than 4% water by weight (0.13% by volume); both were effectively dry within 24 hours. This validates that sorption potential is linked to pore structure, as polyiso has a rigid, solid framework.
- Mineral wool wall CI samples reacted quite differently to rewetting. After seven wetting and drying cycles, mineral wool wall CI water absorption increased by 132%–195% and drying times were extended by up to four days.
- Repeated wetting of mineral wool wall CI revealed moisture holding capacities that vary due to changing pore and fiber structure.
Because polyiso and mineral wool wall CI have historically been evaluated using different methodologies, architects and engineers have a harder time comparing and evaluating potential risks when choosing insulation solutions. Based on the findings that Dr. Doggett reported, previous sorption and drying potentials for mineral wool wall CI have been vastly underestimated. Further evaluation may also determine that the effective R-Values of mineral wool wall CI products are also impacted.
Polyiso has been proven to have low absorption potential and high drying potential, and continued exposure to liquid water does not degrade the structure of the material, as it does mineral wool wall CI.
ABOUT ATLAS® ROOFING CORPORATION
Atlas Roof & Wall Insulation division is a leader in promoting energy efficiency and conservation, and has long been blazing the trail of environmental stewardship. Atlas now has eight top-of-the-line polyiso manufacturing facilities that produce millions of board feet each year. Learn more.
Atlas® Roofing Corporation also manufactures asphalt shingles, roof underlayments, rigid expanded polystyrene, geofoam, cold chain, protective packaging, lost foam, and cutting-edge coated and paper facers and underlayments for a diverse set of markets. Atlas has grown from a single asphalt shingle manufacturing facility to 36 facilities in North America with worldwide product distribution. Products from the company’s four major divisions, Polyiso Roof & Wall Insulation, Shingle & Underlayment, Molded Products, and Web Technologies, are manufactured in state-of-the-art facilities and shipped from its network of manufacturing plants and distribution facilities in the United States, Canada and Mexico.
1Based on the white paper, Mineral Wool and Polyisocyanurate Insulation: A comparative study of water absorption, drying and rewetting by M. Steven Doggett, Ph.D., Principal Scientist, Built Environments, Inc.
2Sorption is a general term in physical chemistry used to describe the combined processes of absorption and adsorption.