Pipe insulation · Elastomeric foam
AEROFLEX Tube Insulation
- Tube bore
- 6–165 mm
- Wall thickness
- 6–50 mm
- Service temp.
- -57 – 125 °C
Closed-cell vs fibrous insulation: what is the difference?
In short
Closed-cell insulation, such as elastomeric foam and PE foam, holds its gas in separate cells, so vapour and water pass through the body with difficulty; it is widely used on cold work where condensation must be prevented. Fibrous insulation, such as glass wool and stone wool, has connected air spaces, so it absorbs sound better and includes grades for high temperatures, but on cold work it relies on a vapour-retarder facing. Neither is better for every job.
How the structures differ
- Closed cell — a foam in which most gas bubbles are sealed from each other; the cell walls stop air flowing through.
- Fibrous — glass or stone fibres entangled into boards or rolls; the air sits in spaces between fibres that are all connected.
Both insulate on the same principle, by keeping air still. The actual thermal conductivity depends on the product, its density and temperature, and must be read from the manufacturer's datasheet (thermal conductivity λ).
Moisture and vapour
| Closed cell | Fibrous | |
|---|---|---|
| --- | --- | --- |
| Vapour through the body | Difficult; resistance is in the material | Passes; relies on a vapour-retarder facing on cold work |
| Points to watch | Joints, slits, ends must be glued | Torn foil facings, untaped joints |
| If wetted | Little water enters the body, per manufacturer data | Moisture can collect in the body and performance drops |
Each product's vapour resistance is given as a value tested to a standard, such as ASTM E96 or a μ value to EN 12086; compare only values tested the same way. Read more: what is a vapour barrier.
Sound: absorption vs closed cell
Sound is absorbed when sound waves enter connected air spaces and lose energy through friction. That is why fibrous insulation is widely used as a sound absorber, for example as duct liner or inside walls. Closed-cell insulation lets much less sound into its body, so it is not designed mainly for sound absorption.
If you need absorption, check the NRC or absorption coefficients of that product in its datasheet (what is NRC), and remember that absorbing sound is not the same as blocking it (soundproofing vs sound absorption).
Temperature and fire
- Most closed-cell insulation is rubber or plastic, so its service temperature range is limited by its formulation. For example, AEROFLEX tube lists -57 to 125 °C in its datasheet.
- Mineral-fibre insulation includes high-temperature grades; for example, SCG PCI lists 10 to 540 °C in its datasheet.
- Fire behaviour varies widely by material and product. Check the test results in the datasheet, and remember that fire-resistance ratings belong to tested systems, not to a single material (what is service temperature).
Which is typically used where
- Chilled-water pipes and refrigerant lines — usually closed-cell insulation such as elastomeric foam (what is elastomeric foam).
- Ductwork — usually foil-faced glass wool outside, and glass-wool liner inside where noise reduction is wanted; elastomeric sheet is also used.
- Roofs and ceilings — glass wool, stone wool, PE foam and foil-faced elastomeric are all used (what is PE foam).
- Sound absorption in rooms or walls — usually fibrous insulation.
- High-temperature pipes and equipment — usually mineral-fibre insulation rated for the temperature.
Choose by the job, not by the material type
These are broad tendencies. Before choosing, answer: is the surface cold or hot, is there moisture, is noise reduction needed, and are there fire requirements? Then compare values from the datasheets of the products you are considering.
Sources
- ASTM C534/C534M — Preformed Flexible Elastomeric Cellular Thermal Insulation in Sheet and Tubular Form
- ASTM E96/E96M — Standard Test Methods for Water Vapor Transmission of Materials
- EN 14313 — Factory made polyethylene foam (PEF) products for building equipment and industrial installations
- Armacell — information on moisture in closed-cell and open-cell insulation
- NAIMA / Insulation Institute — fibrous-glass duct liner for sound absorption
- Manufacturer documents: AEROFLEX Tube, SCG PCI
Related products
Categories and example products for this topic
- AEROFLEX Tube Insulation — Closed cell: EPDM rubber, vapour permeability below 0.10 perm·in, used on cold pipes
- M-PE (Standard) — Closed cell: PE foam with metalized film for roofs, ceilings and walls
- SCG PCI / PCIF — Fibrous: unfaced glass wool pipe section with a service range up to 540 °C
- Micro Duct Wrap FRK — Fibrous with a vapour-retarding facing: foil-faced glass wool, 0.02 perm max
Building thermal insulation · PE foam
M-PE M-PE (Standard)
- Thickness
- 3–20 mm
- Density
- 35–45 kg/m³
- Thermal conductivity (λ)
- 0.029 W/m·K
Pipe insulation · Glass wool
SCG PCI / PCIF
- Pipe size
- ½–18 in
- Thickness
- 25–50 mm
- Service temp.
- 10 – 540 °C
Duct and HVAC insulation · Glass wool
Microfiber Micro Duct Wrap FRK
- Thickness
- 25–50 mm
- Density
- 16–32 kg/m³
- Thermal conductivity (λ)
- 0.033–0.038 W/m·K