1 FOAMULAR Extruded Polystrene Insulation Resisting Water Absorption, the Key for High Performance Foam Plastic Rigid Insulation Technical Bulletin FOAMULAR Extruded hydrophilic (attracts water), and, Figure 1. Polystyrene Insulation 2) the cell structure must be truly Extruded Polystyrene Cell Structure Owens Corning manufactures a closed. complete line of FOAMULAR . Extruded polystyrene Closed Cell: What it Means Insulation (XPS) products Foam plastics insulate by trapping for use in residential and an insulating gas inside millions commercial construction. The of tiny plastic bubbles, or, cells. primary difference between Insulation that absorbs water Cell Wall Cell FOAMULAR XPS products is into the cells loses R- value. A. foam plastic Insulation that has Figure 2. compressive strength ranging Polyisocyanurate Cell Structure from 15 psi to 100 psi. The a closed cell structure absorbs a variety provides common minimum amount of water thus strength products for use in retaining R-value.
2 Often all foam walls where there is almost no plastic insulations are referred to compressive load; or, intermediate as closed cell . It is important to strength product for use with know what closed cell means modest loads such as around and then relate it to specific foundations, or in low slope Insulation types. Cell Wall Cell roofs; or, high strength product FOAMULAR XPS viewed under Figure 3. Expanded Polystyrene Cell Structure suitable for use under high load a microscope (Figure 1) shows floors or plaza decks. The general a homogeneous cross section FOAMULAR XPS product line of very well defined, uniform has an R-value of 5 per inch of cells with continuous walls. thickness, while faced sheathing The cell walls are comprised of products are available with an R-3 hydrophobic (does not bond with for 1/2 or R-4 for 3/4 thick. water) polystyrene polymer. That Resisting Water Absorption, combination of characteristics, Cell Edge of Bead Air Space the Key for High closed cell/hydrophobic, results in a very low rate of water Expanded polystyrene (EPS).
3 Performance Insulation absorption compared to other Insulation (Figure 3) is comprised The greatest attribute of types of foam plastic Insulation . of polystyrene beads fused FOAMULAR XPS is its ability to together under heat and pressure. retain R-value and compressive Polyisocyanurate Insulation (Figure Although the beads themselves strength even when exposed to 2), by its nature, has a less well are closed cell and hydrophobic, water. Insulation products that defined cell structure, meaning the air spaces between the absorb water lose R-value, and cells tend to be irregular in shape beads allow water and air to structural integrity. Water is a and size and sometimes blended penetrate the board structure. good conductor of energy, so if together. Irregular cells, combined The air spaces between the Insulation is water soaked, R-value with a hydrophilic chemical beads lower the R-value of the is lost. There are two keys for tendency (seeks to bond with board because air has a higher resistance to water absorption: water) results in higher water thermal conductivity than the 1) the plastic itself must be absorption compared to XPS.
4 Insulating gas in the cells. The air hydrophobic (repels water), not spaces also provide a path for FOAMULAR Extruded Polystrene Insulation Resisting Water Absorption, the Key for High Performance Foam Plastic Rigid Insulation Technical Bulletin water penetration, raising water Figure 4. absorption for the complete Water Absorption, XPS vs. Polyiso board. Comparing Properties: What Do They Mean? Published properties for different types of Insulation are not % Volume always directly comparable because different test methods may be used to measure the same properties. If different methods are used to measure performance, identify the differences. They may be significant. XPS Method, ASTM C 272, Polyiso Method, ASTM C 209, Water Absorption 24 Hour Immersed, No Drain 2 Hour Immersed, 10 min. Drain For example, the material standard that defines XPS, Type VI,VII,V. XPS, Type X, IV. Polyiso, Glass Faced Polyiso, Foil Faced properties for all XPS and EPS. is ASTM It requires Figure 5.
5 That polystyrene Insulation be Water Absorption, XPS vs. EPS. tested for water absorption in accordance with ASTM C272 requires the polystyrene sample to be immersed in water for 24 hours, and weighed immediately upon removal from % Volume immersion to determine the amount of absorbed water. The material standard for polyisocyanurate is ASTM It requires that polyiso be tested for water absorption in accordance with ASTM C209 requires the polyiso sample 2 hour 24 hour 7 day 14 day to be immersed in water 2 hours, and drained for 10 minutes before weighing for water absorption. FOAMULAR 250 EPS w/facer EPS, facer removed Figure 4 shows the significant differences in XPS and polyiso water absorption that result FOAMULAR Extruded Polystrene Insulation Resisting Water Absorption, the Key for High Performance Foam Plastic Rigid Insulation Technical Bulletin Figure 6 R-Value & Water Compressive Strength after Water Immersion Absorption 45 Insulation products that absorb 40 water lose R-value.
6 Water is a good conductor of energy, so if 35 Insulation is water soaked, R-value lbs. per sq. in. (psi). 30 is lost. See Figure 7. 25 R-Value & Reflective Foil Facers 20. Some rigid foam plastic Insulation 15 products have foil facers on them that some manufacturers claim 10 add R-value to the wall. The 5 presence of a foil surface can add R-value to a wall if two conditions 0 are FOAMULAR 250 EPS Polyiso Woodfiber 1. The foil must be adjacent to a As Received After 24 Hour Immersion sealed air space; and, 2. The air space must be of from using different measuring Facers also make a difference in uniform thickness, bounded techniques. Note that the water EPS water absorption. Figure 5. by plane, smooth and parallel absorption level for polyiso shows the significant changes in surfaces. increases greatly when tested by the water absorption levels of the same method used for XPS. EPS when facers are removed, If these conditions are not Glass faced polyiso goes from and when immersion time is met, the foil does not provide absorbing 14x more water than increased.
7 Over time, water any increase in R-value. Most XPS, to absorbing 30x more creeps into the spaces between foil faced sheathing is installed water than XPS, when measured EPS beads, lowering R-value and under beveled vinyl or other using the same method. Foil faced raising the risk of beads breaking type of beveled siding, and/or, polyiso goes from absorbing apart with the expansion forces not adjacent to an air space. In more water than XPS, to of freezing and thawing. such situations, the foil does not absorbing over 7x more water provide any increase in R-value. than XPS. Because the presence Compressive Strength &. of foil makes such a difference in Water Absorption R-Value & Test Methods water absorption, the long-term Compressive strength may be Test method differences may durability of the foil is critical. If reduced by water absorption also exist when measuring the foil is punctured or corrodes depending on the make-up R-value. R-value changes as while in service, the polyiso core of the foam plastic Insulation , foam plastic ages.
8 Long term is unprotected from water, and is hydrophobic/closed cell XPS thermal resistance (LTTR) can even more prone to higher water or hydrophilic/more open cell be measured using real-time absorption, like the condition with polyiso. See Figure 6. aging, or aging can be artificially glass facers. accelerated. FOAMULAR XPS. R value of 5/inch is based on real- FOAMULAR Extruded Polystrene Insulation Resisting Water Absorption, the Key for High Performance Foam Plastic Rigid Insulation Technical Bulletin time 5 year aging. The polyiso Figure 7. R-Value Retained in Roof Insulation after Sustained Exposure to Water Vapor 5. industry uses CAN/ULC/S7707, 100. to accelerate aged R-value. The S770 method has been shown to 90. overstate R-value or 80. % R-Value Retained The Misconception of 70. Foam Plastic Insulation as a 60. Double Vapor Barrier 50. If FOAMULAR XPS is used as 40. sheathing on a wall, doesn't that automatically create a double 30. vapor barrier , potentially 20. trapping moisture in the wall?
9 10. The answer is, no. Walls must be assessed for vapor performance. 0. 50 100 150 200 300 400 500 600 700 800 900 1000. The perception is, 1) liquid Foam 250 Polyiso EPS. water runs off of foam plastic Insulation , therefore, 2) it must Exposure Time in Days be water impermeable, and, the misconception, 3) therefore it To control vapor permeation, understanding why FOAMULAR . must be a vapor barrier. buildings in heating dominated XPS is not necessarily a double climates are typically provided a vapor retarder . Vapor condenses in walls for three vapor retarder on the warm in reasons: 1) too much water vapor winter side of the wall. Vapor Although liquid water runs off gets into the wall; 2) it cannot retarders are designed to limit the of, and is virtually unable to escape out the other side fast permeation of interior moisture penetrate, FOAMULAR XPS's enough, and; 3) the accumulating vapor into the wall, where it may closed cell structure, molecules vapor reaches a surface cooler encounter cooler surfaces and of water vapor are another than dew point temperature, condense to liquid as it moves to matter.
10 Water vapor molecules the temperature at which water the lower vapor pressure outside. can pass between the molecules vapor condenses to liquid. Prolonged condensation inside a of any solid material, such as wall assembly can lead to mold FOAMULAR XPS. That process The solutions are, 1) limit vapor is called permeation . The growth. in with a vapor (barrier) retarder; perm rating of a solid material 2) let vapor out faster than it Perm Ratings is the measure of how rapidly gets in; and; 3) make surfaces A vapor retarder limits the it allows water vapor molecules inside the wall warmer using amount of water vapor to pass. The higher the perm . Insulation strategies. This is where permeating into the interior rating, the faster water vapor FOAMULAR XPS helps. side of a wall, so that it is slower passes through. (Keep in mind this discussion is going in than it is going out on about vapor PERMEATION only. the exterior side. Comparing Perm rating varies by thickness, More moisture gets into walls via the perm rating of the retarder decreasing as thickness increases, AIR LEAKAGE, so, that is even more material to the perm rating of with the exception that the important to control than vapor.