Duct, Pipe & Thermal Insulation

Because a below-dew-point line drives water vapor inward. When a surface sits below the ambient dew point, moist room air is pushed toward the cold pipe, so the insulation has to do two jobs at once: slow the heat gain (thermal conductivity per ASTM C177/C518) and resist that vapor drive along its whole thickness (water-vapor permeance per ASTM E96), behind a continuously sealed boundary.

If the wall is too thin, the material more conductive than assumed, or the boundary breached, a point on or inside the wall falls below the dew point and vapor condenses there, wetting the insulation and collapsing its R-value. That is why the controlling numbers on the cold side are the dew point and the permeance, not R-value alone. [6]

From the vendor condensation-control table for your design conditions, not a generic table. The thickness needed to keep the surface above the dew point depends on the design pipe temperature, the ambient temperature, and the relative humidity, so those three inputs pick the thickness for a given material. Being short by as little as ~0.25–0.50 in. can drop the surface below the dew point and start condensation even with a good closed-cell elastomeric.

Send the service temperature and the design dew point (or ambient temperature and RH), and H-O confirms the material class and that the specified thickness and a continuous vapor boundary keep the surface above the design dew point; the sizing result belongs to the installed building. [14]

A closed-cell elastomeric foam (EPDM or nitrile) has a very low water-vapor permeance in its own right, so the material is the vapor retarder, and a correctly sized, continuously sealed wall usually needs no separate barrier on indoor runs. The emphasis then shifts to sealing: seams, fitting collars, and terminations must be closed vapor-tight, because the weakest 5% of the surface governs.

On a fibrous-glass or faced system it is different, the low-perm facing (ASTM C1136) and its sealed seams carry the boundary, and the facing carries the perm rating. So: closed-cell elastomeric, seal the wall; faced fibrous, seal the facing. [3]

25/50 is a flame-spread index of 25 or less and a smoke-developed index of 50 or less, measured per ASTM E84 (equivalently UL 723), the Steiner Tunnel test. It is the common building requirement for materials installed in ducts and plenums, set by NFPA 90A (and NFPA 90B for warm-air heating), and it corresponds to Class A / Class 1.

The index belongs to the tested material grade and is reported on the maker TDS; the requirement attaches to the location, and the code compliance belongs to the installed building. Confirm any 25/50 requirement for your duct or plenum location and read the index off the grade TDS. [7]

Both are steady-state methods that report k and R at a stated mean temperature; the difference is the apparatus and the use. ASTM C177 is the guarded-hot-plate method, the reference/precision technique used for design data. ASTM C518 is the heat-flow-meter method, faster and used for production QA and routine comparison. Because k rises with temperature, a k value only means something with its mean temperature, so cite the method and the mean temperature together.

For a spec, either method is acceptable as long as the value is reported at the mean temperature that matches your service. [4]

Water-vapor transmission is measured per ASTM E96, by the desiccant (dry-cup) or water (wet-cup) method, and reported in perms (grain per hour per square foot per inch of mercury), or, for a material, in perm-inch (permeability). On cold service the low permeance of a closed-cell elastomeric is the vapor retarder; on a faced product the facing carries the perm rating. Cite the method (dry vs wet cup) and the perm value from the grade TDS, because the two cup methods can give different numbers. Lower perm means a tighter vapor boundary. [6]

Both EPDM and nitrile are closed-cell elastomerics whose low permeance is the vapor retarder; the split is exposure and cost. EPDM is the weather- and UV-tolerant default, the better choice where the line runs exposed outdoors. Nitrile (NBR / PVC-NBR) is the oil-resistant, economical option for indoor and mechanical-room cold lines. Silicone foam is not primarily a cold-service material: it comes in on the hot side and in plenums, where the widest temperature range and UL 94 V-0 grades matter, or where a hot connection gasket needs a flame class.

Match the family to the service temperature and the exposure, and confirm the class on the grade TDS. [1]

Both, plus the air velocity. A fibrous-glass duct liner does two jobs, cutting conductive heat gain or loss through the sheet metal and absorbing fan and airflow noise, and ASTM C1071 catalogues what it must deliver: apparent thermal conductivity, sound-absorption coefficients, erosion resistance, water-vapor sorption, and combustion characteristics, for air to 250 °F. The third input is the system's air velocity, because the liner surface must withstand it without eroding or shedding fibres, verified per UL 181.

Where a wipeable, non-fibrous surface is required (labs, healthcare, wash-down), a closed-cell foam liner is the alternative. Send the duct dimensions and the design air velocity, and the liner and its edge treatment follow. [2]

No part is, and no honest supplier will claim otherwise or call one "fireproof". What the materials carry is their own documentation: material-level classes such as a thermal conductivity (k per ASTM C177/C518), a water-vapor permeance (per ASTM E96), a 25/50 surface-burning index (per ASTM E84), an ASTM C534 / C1071 conformance, and a UL 94 class, all on the grade TDS, plus lot-code traceability.

The code compliance (NFPA 90A), the system rating, and the finished condensation-control result belong to the installed building, cited by designation. H-O supplies the converted part and the paperwork; the installed system carries the compliance. [10]

Corrosion-under-insulation is the corrosion of the pipe surface that happens when condensate is trapped against cold metal under a breached or undersized insulation system. On a below-dew-point line with a broken vapor boundary, vapor driven inward reaches the cold pipe and condenses; the trapped moisture wets the insulation, drips, and corrodes the pipe over months and years, out of sight.

The spec prevents it the same way it prevents sweating: size the wall to the design dew point, choose a low-permeance closed-cell material, and seal the vapor boundary continuously at every seam, collar, and termination so vapor never reaches the cold metal. That continuity at the fittings is why the collars and closures are parts, not field offcuts. [1]

Yes: die-cut collars, wraps, saddle pieces, liner pieces, gaskets, and closure strips can ship as kitted sets, sized to a run of fittings, parts on liner in install order, with lot-code TDS records per material. Kitting the fitting parts is exactly how the vapor boundary stays continuous at the weakest 5% of the surface, because the collars at valves and elbows and the closures at terminations arrive as parts instead of field-trimmed gaps.

H-O die-cuts, kiss-cuts, waterjet-cuts (thick sections), slits, and laminates (foam-plus-facing or foam-plus-scrim stacks) to drawing. [3]

H-O and converts sheet, roll, and tubular stock to drawing; molding and extrusion are not in-house services, and extruded profiles are coordinated through a partner network (made-to-order, 4–6 week tooling). Conversion runs in Winsted, Connecticut under an ISO 9001:2015 certified quality management system with material traceability and lot-code TDS records. What ships is custom, made to order to your pipe run, duct size, or connection detail.

H-O is a die-cutter and converter, not a stocking distributor of finished insulation, with multiple working material relationships across the elastomeric, glass-fibre, silicone, and PE families. [13]