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EPDM, Silicone Sponge, or Fluorosilicone: Choosing Gaskets and Insulation for CDU and RDHx Hardware

By the H-O Products applications engineering team · Updated June 2026 · ~9 min read

Liquid-cooling material selection starts with two questions: what fluid can reach the seal, and where does the part live? A dry-side CDU door gasket never wets, so EPDM foam economics win. A coolant manifold penetration sees glycol mist and the occasional weep, which moves the seal to fluorosilicone sponge. An immersion tank gasket lives in the dielectric fluid itself, which points to FKM with FFKM held for the most aggressive chemistries.

And pipe insulation is bought by the degree: the aerogel grade follows the line temperature against the room dew point. This guide walks the selection the way the parent application page structures it, family by family, with compression-deflection cited per ASTM D1056, thermal conductivity per ASTM C177, flame listings per UL 94 on each grade TDS, and per-grade values left on the TDS where they belong.

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Dry-side gaskets: the EPDM and neoprene economics

RE-series closed-cell EPDM foam (RE41E through RE45E, with the 553 and 563 solid grades beside it) is the general-economics gasket of the cooling plant: CDU doors, access panels, and containment-adjacent joints that stay dry and carry no flame-class callout. For the long perimeter runs of hot and cold aisle containment, where quantities are large and the duty is indoor and dry, SCE-series neoprene foam is the lower-cost mapping (UL 94 HF-1 data on the SCE TDS), with EPDM beside it where UV- or ozone-adjacent service appears.

The discipline in this zone is dimensional rather than chemical: measure the real joint gaps, pick the firmness so panels and doors still latch, and cut strip widths to the panel system on the drawing. Every joint that leaks is bypass airflow the cooling plant pays for.

Fire-rated and high-cycle joints: the silicone track

Two conditions move a gasket off the economy track. First, the flame rating: when the enclosure specification calls UL 94 V-0 on seal materials, unrated foam leaves the candidate list at any price. The kSil V-0 silicone sponge range (see the kSil V-0 70 product page) and the RS-series silicone sponge (RS-800 medium default, softer and firmer siblings) carry V-0 listings on their TDSs, verified at your thickness during drawing review.

Second, the duty cycle: an RDHx door opens and closes thousands of times, much of it warm, and an organic foam that tested fine at commissioning gradually takes a permanent set until hot exhaust starts bypassing the coil. Silicone's flat compression-set behavior across temperature is why BISCO silicone foam (BF-1000 Extra Soft and its ultra-soft sibling, with the HT series stepping firmer) owns the RDHx frame-to-rack gasket, matched to the door's real closure force so the gasket works at mid-deflection.

Compression-deflection and set are reported per ASTM D1056 on each TDS.

Fluid-exposed seals: fluorosilicone, FKM, and FFKM

Chemistry takes over the moment coolant can reach the seal. At glycol-exposed manifold penetrations, standard silicone sponge is a poor match for sustained exposure; the cautious choice is fluorosilicone sponge (AMS 3323 family), which keeps silicone's cellular conformance while adding the fuel and chemical resistance.

In immersion cooling, every tank seal lives in continuous contact with the dielectric fluid, and elastomer selection follows the fluid, not the fixture: FKM fluoroelastomer (75 durometer solid, with Viton sponge where a conformable closed-cell form suits low closure force) is the working family for the common synthetic-ester and hydrocarbon fluids, and FFKM is the step-up where the chemistry margin is in question.

In every case the pairing is confirmed against the fluid maker's elastomer compatibility data for the specific fluid: swelling, hardness change, and extractables matter more than any single headline number.

Pipe insulation: three aerogel grades, split by line temperature

Cryogel Z, ArmaGel HT/HTL, and Pyrogel XTE are all "aerogel blanket" on a data sheet, and specifying the warm-line grade on a chilled line is a condensation problem, not a heat-loss problem. Cryogel Z is the sub-ambient grade for below-dew-point chilled lines, where the job is keeping the jacket surface above the room dew point and resisting water-vapor drive (characterized per ASTM E96 on the TDS), with the vapor-control jacket and seam sealing detailed on the drawing.

ArmaGel HT and HTL are the thin, flexible default for the warm supply and return runs that make up most of the loop, die-cut cleanly into fitted sleeves, saddles, and manifold blankets. Pyrogel XTE takes the hottest return and reclaim lines; the parent page notes the family is rated for service to 650 °C, far above any coolant loop, so the margin is in the material rather than the installation.

Conductivity is per ASTM C177 and surface burning per ASTM E84 on each TDS; thickness is sized from the TDS values for your line and ambient.

The two system companions: the vent and the pads

Two parts finish the CDU cabinet. A tightly gasketed enclosure thermal-cycles with the loop, and with no engineered vent it inhales humid room air through whatever path yields first, then condenses that moisture on the coldest internal surface; a die-cut ePTFE vent membrane patch equalizes the pressure swing while blocking liquid water, sized from the membrane maker's airflow data for the enclosure volume.

And the pump skid rides on microcellular urethane pads (PORON industrial 4701/4790 series) whose low compression set per ASTM D3574 keeps the isolation working years in; treat the pad as a spring and state the supported mass and footprint so the firmness grade loads into its working range instead of bottoming out.

How H-O Products helps

H-O Products is a precision die-cut converter, not a raw-material producer. We die-cut, kiss-cut on liner, slit, and laminate gasket, foam, sponge, aerogel, membrane, and elastomer sheet stock to your drawing: door and panel gaskets, long containment perimeter strips, fitted insulation sleeves and manifold blankets, vent patches, and pump pads, with material traceability and lot-code TDS records under our ISO 9001:2015 certified quality management system in Winsted, Connecticut.

Everything is made to order. We recommend family and grade direction against your fluid, fire rating, line temperature, and seal locations, and we verify grade data against the maker's current TDS; extruded or molded profiles are coordinated through our partner network.

Frequently asked questions

Related reading

ApplicationData Center Cooling & Liquid InfrastructureRead → Sub-applicationData Center Sealing & AirflowRead → GuideGlycol, Dielectric Fluids, and the Seal: Coolant-Loop Elastomer Compatibility on a DelayRead → GuideHow to Spec Liquid-Cooling Seals and Pipe Insulation: What to Send H-O for a QuoteRead → IndustryElectromechanical & Switchgear hubRead →

Last updated June 2026 · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).

References

• ASTM D1056 (flexible cellular rubber, compression-deflection classes); UL 94 (V-0 and HF-1 listings, per grade and thickness); ASTM D3574 (cellular urethane methods).
• ASTM C177 (aerogel thermal conductivity); ASTM E84 (surface burning); ASTM E96 (water vapor transmission, sub-ambient insulation); AMS 3323 (fluorosilicone sponge designation); ASHRAE TC 9.9 datacom liquid-cooling guidance (facility-water classes, cited qualitatively).
• Maker technical data sheets: RE-series EPDM; SCE-series neoprene; kSil V-0 and RS-series sponge; BISCO BF / HT-series silicone foam; fluorosilicone sponge; FKM 75D and Viton sponge; FFKM grades; Cryogel Z; ArmaGel HT/HTL; Pyrogel XTE; ePTFE vent membrane; PORON industrial urethanes.

This article summarizes material-selection principles for liquid-cooled data center infrastructure using the published standards and material families named above. Comparisons are qualitative; per-grade compression, conductivity, and flame data must be confirmed on the maker's current technical data sheet, and fluid compatibility against the fluid maker's data for the specific fluid. Flame listings belong to the listed grades; facility-level requirements belong to the facility engineering.

All parts are custom manufactured to order; minimum production run quantities vary by material and part. H-O is a die-cut converter, not a raw-material producer.