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Insulation & Composite Foam Cores

Polyiso vs. Calcium Silicate Pipe Insulation for Temperatures up to 350°F (176°C)

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Dyplast’s Qwik Guides are intended to provide a brief, one-page summary of important technical issues. The objective of this Qwik Guide is to address the temperature range [generally from ambient temperature up to +350°F (176°C)] where Polyisocyanurate and Calcium Silicate may compete.

This temperature range encompasses the domain of condensate, hot water, low-temperature steam, and chemical/pharma process. The question becomes “Why use CalSil when Polyiso is a much better thermal insulator and has a significantly lower material cost, dramatically less weight, and lower installed costs?”

CalSil versus Polyiso Pipe Insulation


  • Polyisocyanurate (ISO-C1®) has 50% better thermal insulation properties than the best CalSil suppliers at 200°F.
  • ISO-C1/2.0 Polyiso is roughly half the cost of CalSil pipe insulation per linear foot at the same thickness.
  • CalSil requires thicker pipe segments since it has poorer R-values, thus almost doubling the volume required.
    • Thicker applications mean more shipping weight/volume and storage volume prior to installation, more jacketing, and tighter spaces between pipes.
  • The weight of CalSil is 7.5 times more than ISO-C1/2.0, and 6 times more than ISO-HT.
    • CalSil insulation, 2 inches thick, on 3 linear feet of 3-inch IPS pipe, could weigh 15 lbs; while ISO-C1/2.0 may require only 1 or 1.5-inch thickness (depending on process temperatures), and would weigh only 1.2 to 1.8 lbs; thus, the Polyiso would require fewer pipe hangars, less vapor barrier, jacket, etc.
  • The weight of CalSil combined with its fragility makes it subject to breakage, potentially further increasing installation costs.
  • At below-ambient temperatures there is a probability of condensation, so CalSil is problematic given its high water absorption and water vapor transmission properties.

Please read more in our one-page Qwik Guide.

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