Insulation Materials: Cellular Polyolefin
Polyolefin closed cell tubular insulation was developed in Europe in the 1970s. Much of the development work was done in Belgium. It was first introduced in the United States in 1979 as a do-it-yourself insulation in semi-slit, three-foot lengths. During this time, the country was undergoing our first energy crisis, with government rebates for home insulation improvement, so polyolefin insulation quickly caught on as a pipe insulation for domestic hot and cold water.
During the early 1980s, a preslit/preglued product was introduced and polyolefin insulation was brought to the commercial market for hot and cold water, drain pipes, and other applications. The market migrated to the preslit and preglued, 6-foot product as the main product offered in ⅜ -, ½-, ¾- and 1-inch wall up to 4-inch iron pipe size (IPS) IDs. Further advances of the product into lower-temperature applications, including cryogenic industrial applications, came in the late 1990s. Although it has found successful applications in the industrial market, the primary market for polyolefin insulation continues to be plumbing—hot and cold water, and roof drains.
The Manufacturing Process
Polyolefin closed cell tubular insulation is predominately comprised of polyethylene resin, which is one of many resins in the polyolefin family. For this reason, the product is also often referred to as polyethylene insulation. Other resins in the family would be polypropylene and ethylene vinyl acetate. Polyethylene resin has a very sharp melting point, and this characteristic is key to the manufacturing of the product.
To begin the manufacturing process, polyethylene resin pellets are fed into an extruder along with other ingredients such as UV and heat stabilizers, colorants etc, which are also in pellet form. All of these materials are melted and blended together.
In the second phase of the extrusion process, a physical blowing agent (typically a hydrocarbon), which is in the form of a gas, is injected into the extruder under high pressure and blended into the molten mixture. The material is under pressure in the extruder as it is pushed through a die at the end of the extruder, forming the tubular shape. The die consists of an outer ring with a pin in the center that forms the ID of the tube. As the material exits the die, it immediately expands as the blowing agent normalizes the pressure. Because the mixture exits the forming die at a temperature very close to the melting point of the resin, it quickly sets up or solidifies and maintains its cellular structure rather than collapsing its shape. The material is then cooled down completely, cut to length and packaged.
The product can be slit and pressure-sensitive adhesive can be applied to the seam, if requested, during the cooling process. The process runs quickly, and there is little waste. Any scrap generated during the manufacturing process can be recycled back into the process since the material remains a thermoplastic and it can be remelted.
The majority of polyolefin insulation sold is in tubular form. The current preformed size limitation is 4-inch IPS x 1-inch wall. The product can be sleeved to achieve greater wall thicknesses. Manufacturing methods are currently under development to expand both the ID and wall size range.
The product gets its physical property characteristics from its base resin (polyethylene) and the fact it has a closed-cell structure. Polyethylene resins offer great water, chemical, and abuse resistance as evidenced by its other applications, such as beverage containers, trash bags, life jackets, and other consumer items. The closed-cell structure of polyolefin insulation also provides its thermal properties (k value).
Polyolefin insulations are identified by American Society for Testing and Materials (ASTM) C 1427. They are suited for applications within a temperature range of -150°F to 200°F, which fits well with their primary application of hot and cold water lines, as well as roof drains. Polyolefin insulations have low water-vapor permeability characteristics, as evidenced by a water vapor transmission (WVT) permeability rating of .05 perm-inch max. Caution does need to be taken not to use these materials on above ambient temperatures applications above 200°F.
Polyolefin insulations are easy to work with. No special tools or protective clothing are required. The most predominantly used form is preslit/preglued, which almost eliminates the need for additional adhesives on most jobs. It can be easily fabricated in the field with a sharp knife.
Common applications include the following:
- Hot and cold water (domestic and commercial)
- Roof drains
- Cold process pipes and equipment
- Heating, ventilating, and air-conditioning (HVAC) equipment
Specific physical properties of the material can be found on the National Insulation Training Program (NITP) chart at www.insulation.org/techs/MaterialsSpecs.pdf under Polyolefin Sheet and Tube.
Additional information can be found in the Manufacturers’ Technical Literature (MTL) Product Catalog at www.insulation.org/mtl or on specific manufacturers’ websites.
Readers who are interested in learning more about the insulation material featured here should visit the MTL Product Catalog at www.insulation.org/MTL or visit the NIA Membership Directory at www.insulation.org/membership to find a manufacturer.
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