ISO-HT® Polyiso Datasheet

ISO-HT®    Polyisocyanurate Insulation
2.5 lb/ft³ (40 kg/m³) density for Higher Temperature Applications

ISO-HT is Dyplast Products’ 2.5 lb/ft³ polyisocyanurate rigid, closed cell, foam insulation for higher temperature applications up to 350°F (177°C), with intermittent exposure up to 375°F (190°C). ISO-HT is suitable for constant temperature or heat cycling environments. ISO-HT is certified by independent laboratory to meet demanding Class 1 flame spread and smoke development requirements per ASTM E84. ISO-HT fully complies with the demanding requirements of ASTM C591-15. Dyplast offers ISO-HT as bunstock or as sheets and blocks, with tolerances up to 1/32 inch on surfaces. Our extensive network of fabricators can provide special shapes for pipe, fittings, vessels, or other mechanical applications.

Polyisocyanurate exhibits the highest R-factor (insulating value) to thickness ratio of commercially available insulation, and ISO-HT provides higher R-factors and reduced thermal aging at lower temperatures. Ideal for applications over a wide range of temperature, from cryogenic liquids to low-temperature steam, ISO-HT offers superior performance when compared to polystyrene, polyurethane, phenolic,fiberglass, and cellular glass alternatives. When temperatures are limited to less than 300°F, our ISO-C1 product line is also available in 2, 2.5, 3, 4, and 6 lb/ft³ densities, which each provide successively improved strength and other attributes for physically demanding applications.

Dyplast’s ISO product line is produced as a continuous foam bunstock. For specific standard stock bun sizes contact the sales department.


ISO-HT is designed for use where temperatures range from -297°F to +350°F, making it ideal for low-temperature steam applications and refinery liquids, as well as commercial refrigeration, HVAC, chilled water, and hot water systems, panel insulation for transportation containers, and core material for architectural and panel construction.


Water absorption by insulation can degrade thermal insulating performance. ISO-HT’s extraordinary resistance to water absorption (0.6%) helps ensure long-term thermal performance remains superior to polystyrenes, phenolic foams, fiberglass, and even cellular glass - - which for example has water absorption of 0.2% (per manufacturer data), as well as considerably lower insulating value. Proper installation of vapor barriers can further improve performance of the complete ISO-HT insulating system.


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Dyplast Products is the preeminent manufacturer of polyisocyanurate and expanded polystyrene rigid foam products. With world-class production facilities in Miami, Florida, Dyplast Products offers its customers unsurpassed technology, responsiveness, wide-ranging product configurations, and state-of-the-art quality control. Our customer-focused staff, combined with our sound financial footing, ensure we deliver incomparable value to our customers far into the future. For information on Dyplast Products or additional technical data on this product, visit our website at


The International Mechanical Code defines Class 1 insulation as meeting the 25/450 flame spread/smoke development rating. ISO-HT performs well within this range with a 25/400 (at 4”) rating. When comparing surface burning characteristics of alternative products, care must be taken to consider the installed insulation system as a whole, including sprinkler systems. For example, a well-designed ISO-HT insulation system can improve overall flame/smoke performance of the polyiso insulation. On the other hand, an alternative insulation’s flame/smoke ratings may be compromised by the sealants or jacketing often recommended by suppliers. There is also the matter of insulation system integrity during a fire. ISO-HT may be charred by flame, but maintains its integrity and continues to protect the insulated system.


High thermal insulation effciency is achieved by infusing cells with gases having low thermal conductivity. All such rigid foam insulation (including polyurethane, extruded polystyrene, and polyisocyanurate) thus lose a small amount of their insulating value over time as air displaces insulating gases. ISO-HT’s smaller, stronger cell structure and our proprietary cell-gas formulation work together to impede gas transfer across cell boundaries, thus reducing loss of thermal effciency. At a testpoint of 75°F, the average R-factor of ISO-HT over a 15 year period is comparable to the six-month “aged” R-factor. Thicker insulation, vapor barriers, and metal constraints also limit gas diffusion. Current LTTR calculation standards are primarily applicable to “faced” polyiso board, and are not appropriate for ISO-HT bunstock.


 ISO-HT is designed for constant temperature exposure up to 350°F. ISO-HT should be installed on pipe at room temperature and installation onto high temperature or live steam lines is discouraged, since this will cause dimensional stability problems. ISO-HT should be used with an appropriate ASJ or Vapor Barrier held in place with SSL tape. The use of ¾ inch filament tape with a 25% overlap is recommended, as is a PVC or Metal Jacket secured with metal banding.