Division 7 Ebook Page 535 FOAMULARŪ XPS Insulation Resisting Water Absorption (Comparing Types of Rigid Foam Plastic Insulation)

Technical Bulletin FOAMULAR Extruded Polystrene Insulation Resisting Water Absorption, the Key for High Performance Foam Plastic Rigid Insulation FOAMULAR Extruded Polystyrene Insulation Owens Corning manufactures a complete line of FOAMULAR extruded polystyrene insulation (XPS) products for use in residential and commercial construction. The primary difference between FOAMULAR XPS products is compressive strength ranging from 15 psi to 100 psi. The variety provides common strength products for use in walls where there is almost no compressive load; or, intermediate strength product for use with modest loads such as around foundations, or in low slope roofs; or, high strength product suitable for use under high load floors or plaza decks. The general FOAMULAR XPS product line has an R-value of 5 per inch of thickness, while faced sheathing products are available with an R-3 for " or R-4 for " thick. Resisting Water Absorption, the Key for High Performance Insulation The greatest attribute of FOAMULAR XPS is its ability to retain R-value and compressive strength even when exposed to water. Insulation products that absorb water lose R-value, and structural integrity. Water is a good conductor of energy, so if insulation is water soaked, R-value is lost. There are two keys for resistance to water absorption: 1) the plastic itself must be hydrophobic (repels water), not hydrophilic (attracts water), and, 2) the cell structure must be truly closed. Closed Cell: What it Means Foam plastics insulate by trapping an insulating gas inside millions of tiny plastic bubbles, or, cells. Insulation that absorbs water into the cells loses R-value. A foam plastic insulation that has a closed cell structure absorbs a minimum amount of water thus retaining R-value. Often all foam plastic insulations are referred to as "closed cell". It is important to know what "closed cell" means and then relate it to specific insulation types. FOAMULAR XPS viewed under a microscope (Figure 1) shows a homogeneous cross section of very well defined, uniform cells with continuous walls. The cell walls are comprised of hydrophobic (does not bond with water) polystyrene polymer. That combination of characteristics, closed cell/hydrophobic, results in a very low rate of water absorption compared to other types of foam plastic insulation. Polyisocyanurate insulation (Figure 2), by its nature, has a less well defined cell structure, meaning cells tend to be irregular in shape and size and sometimes blended together. Irregular cells, combined with a hydrophilic chemical tendency (seeks to bond with water) results in higher water absorption compared to XPS. Expanded polystyrene (EPS) insulation (Figure 3) is comprised of polystyrene beads fused together under heat and pressure. Although the beads themselves are closed cell and hydrophobic, the air spaces between the beads allow water and air to penetrate the board structure. The air spaces between the beads lower the R-value of the board because air has a higher thermal conductivity than the insulating gas in the cells. The air spaces also provide a path for Figure 1 Extruded Polystyrene Cell Structure Cell Wall Cell Figure 3 Expanded Polystyrene Cell Structure Cell Edge of Bead Air Space Figure 2 Polyisocyanurate Cell Structure Cell Wall Cell

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