Blanket Insulation Materials: Using Fiberglass & Pyrogel Together

2” of type E needled fiberglass VS. 1” of 10mm of Pyrogel XT + Type E needled fiberglass

e needled fiberglass

Type E needled fiberglass

Pyrogel Insulation Material

Pyrogel XT







Fiberglass is a popular material choice for removable insulation jackets. Another is silica aerogel, aka Pyrogel. We’ve compared needled fiberglass to Pyrogel before. However, the choice needs not be confined to one or the other: you can use both.

In fact we’ve found that, for most “box-type” insulation jackets, the best choice of blanket insulation material is 1 inch of Type E needled fiberglass together with 10mm of Pyrogel XT. Let’s compare this to 2 inches of E needled fiberglass only.

Factors to consider when comparing insulation material performance include: durability, flammability, weight, ease of handling, moisture absorption, and (of course) heat retention.

Both insulation materials are durable, non-combustible, and safe to be around. Let’s compare the other characteristics using the example of typical 6-inch 125 lb. gate valve.

Jacket weight and handling

For our 6” 125lb gate valve, we have 5.04 square feet of surface area. This requires 10.59 square feet of insulation material. 2” Needled fiberglass weights about 1 pound per square foot. Pyrogel XT weighs 0.41 pounds per square foot.


  • 2” of type E needled fiberglass gives a total jacket weight of 21.18lbs.
  • The jacket with 1” E needled fiberglass and 10mm of Pyrogel XT weighs in at 14.82 lbs.

The fiberglass-only jacket was 43% heavier. This extra material has several possible issues. First, it may be undesirable to put the unwanted stress of additional weight on some components. Additionally, the bulkier jacket may be difficult for personnel to handle in tight areas. This can be a safety concern if hot un-insulated pipes or valves are nearby. Also, many steam components are located in high areas, and it is a safety issue for personnel to handle heavy weight when on an 8 foot or taller ladder.

All other things equal, a lightweight insulation jacket is superior.

Advantage: fiberglass/Pyrogel

Heat retention

Let’s compare thermal performance on that valve. Assume 75 °F ambient temperature and 0 mph wind speed for the 6” 125lb. gate valve at 100psig (pound/square inch) steam pressure. Note that 100psig steam has a temperature of 337.9°F and this valve has 5.04 SF of surface area.

Thickness BTU/Hr./SF Lost – Bare BTU/Hr./SF Lost – Insulated Touch Temp. Efficiency
2” E Needled Fbgls 1320 85.84 94.2°F 93.5%
1” E Fbgls & 10mm Pyrogel XT 1320 93.55 98.2°F 92.9%

Calculated out using a figure of $10.00/MMBTU, the yearly difference in energy expenditures on our gate valve is $0.68.

Advantage: negligible

Moisture Absorption

Fiberglass insulation must be kept dry. Wet fiberglass insulation may be at risk for mold and may also contribute to corrosion under insulation. Furthermore, fiberglass that has become wet has a drastically reduced thermal efficiency.

However, Pyrogel XT is breathable yet completely hydrophobic and will not allow moisture to get to the fiberglass insulation. Thus, the biggest advantage of Pyrogel/fiberglass insulation is that between the outer portion of the jacket and the inner fiberglass insulation we now have a completely hydrophobic barrier in place.  External moisture infiltration is now no longer a problem. The result is reduced risk of mold and corrosion under insulation and an insulation jacket that whose heat retention capability does not break down in a damp environment.

Advantage: fiberglass/Pyrogel

It’s plain to see that an insulation jacket with both fiberglass and Pyrogel material is superior to a fiberglass-only jacket.

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