Sealing refrigerants
and cooling systems —
what the material data confirms
High compressibility and recovery can make it relevant for compressor flanges and cooling system joints where face condition is variable and bolt load may be constrained. Specific compatibility should be verified against the chemical resistance chart for the FLEXSEAL PRO 350 grade and the actual refrigerant and compressor oil combination in service.
Documentation scope: Approval, compliance and certification references apply to the documented material grade, supplier certificate or listing, and stated test conditions unless a product-specific certificate says otherwise. A cut gasket size is not automatically certified as a separate product just because it is made from a documented material. For regulated applications, confirm the current certificate or listing scope, exact grade, medium, temperature, pressure and market requirement before specifying.
Scope note: This article is an application-selection reference. Final gasket choice depends on the exact medium, oil or glycol chemistry, concentration, pressure, temperature, flange condition and any site or regulatory requirement.
What the material data confirms
FLEXSEAL PRO 350 is a synthetic fibre + NBR binder gasket grade. The technical datasheet (April 2026 revision) lists the following media and application areas:
- Media: mineral oils, fuels, lubricants, refrigerants, steam, air, and many other media
- Application areas: Compressors & Pumps, Refrigeration & Cooling, Heating Systems, Valves, Shipbuilding, Automotive and Engine Building
Source: FLEXSEAL PRO 350 gasket material datasheet, Kinetics Line, April 2026
Key material properties relevant to refrigeration applications
| Property | Value | Standard | Relevance |
|---|---|---|---|
| Compressibility | 25% | ASTM F36J | Accommodates flange face irregularities — relevant on compressor flanges subject to vibration |
| Recovery | 64% | ASTM F36J | Maintains sealing contact after compression — important under thermal cycling |
| Specific leak rate | 0.009 mg/(s·m) | DIN 3535-6 | Comparative tightness data under the stated test method; refrigerant-side suitability still requires review against the actual refrigerant, lubricant, pressure and project requirement |
| Peak temperature | 350°C | — | Well above compressor discharge temperatures in most refrigeration systems |
| Continuous temperature | 250°C | — | Covers high-side compressor operating conditions |
| Max pressure | 100 bar | — | May cover some high-pressure refrigerant duties within the material and joint design envelope; verify actual high-side pressure, temperature and flange standard |
| Residual stress at 300°C | 20 MPa | DIN 52913 | Retains bolt load at elevated temperature — relevant at compressor discharge |
Where FLEXSEAL PRO 350 is appropriate in cooling systems
Compressor flanges
Compressor inlet and discharge flanges are subject to vibration, pressure cycling and elevated temperatures at the discharge side. High compressibility allows the gasket to conform under variable bolt loads. The material is listed for compressors and pumps in the TDS.
Refrigerant pipework flanges
Flanged connections on refrigerant pipework — suction and discharge lines — operate at lower temperatures but require tight sealing. The published leak-rate value and refrigerant media listing support assessment for this application, provided the actual refrigerant, lubricant, pressure and flange design match the material data.
Cooling system valves
Valve body gaskets in refrigeration and cooling circuits. The TDS lists Valves as a confirmed application area alongside Refrigeration & Cooling.
Heat exchanger flanges
Heat exchanger flanges in cooling circuits — condensers, evaporators — where the gasket may see refrigerant on one side and water or air on the other. Both media are listed as appropriate for the FLEXSEAL PRO 350 grade.
Why compressibility matters here
Standard lower-compressibility fibre gaskets — designed for static piping with clean, well-finished flanges and full bolt load — can be less forgiving on compressor flanges. Compressor flanges may have:
- Residual surface irregularities from machining or long service
- Lower available bolt load due to flange design constraints
- Vibration that can work a stiffer gasket loose over time
- Thermal cycling between ambient and operating temperature on start and stop
At 25% compressibility, FLEXSEAL PRO 350 has a higher sealing margin on imperfect faces than stiffer aramid or graphite grades. The published 64% ASTM F36 recovery describes short-duration recovery under that test method; it does not by itself demonstrate long-term retained stress or thermal-cycle performance. FLEXSEAL PRO 350 is specifically developed, per its technical data, for applications where low bolt loads are permissible and flange irregularities need to be compensated.
Field check: Before specifying FLEXSEAL PRO 350 on a refrigerant-side joint, identify the refrigerant, compressor oil, high-side and low-side pressure, minimum and maximum temperature, flange standard, gasket thickness and face condition. Do not approve the gasket from the word "refrigerants" alone. The final check is the exact refrigerant-oil combination against the Kinetics Line technical data and project requirement.
What to verify for a specific refrigerant
The FLEXSEAL PRO 350 technical data lists "refrigerants" as a media category. This generic listing covers a broad class of compounds but does not individually specify every HFC, HFO, HCFC, ammonia or CO₂ system refrigerant. Before specifying FLEXSEAL PRO 350 in a refrigerant application, the following should be confirmed:
- Refrigerant and lubricant combination: check the exact refrigerant together with the compressor oil in service. POE, PAG, mineral oil and alkylbenzene systems can change material compatibility, so the refrigerant name alone is not enough.
- Chemical resistance chart: A chemical resistance chart is published for the FLEXSEAL PRO 350 grade (referenced in the technical data). This chart rates compatibility by refrigerant compound and should be consulted for the specific refrigerant in service — R410A, R32, R134a, R744 (CO₂), NH3 and others each have distinct chemical properties.
- Operating pressure and temperature: confirm the system high-side and low-side conditions against the supplier's pressure-temperature guidance. The published 100 bar maximum pressure and 250°C continuous temperature are separate maxima and must not be combined as a rectangular operating envelope.
- CO₂ / R744 systems: transcritical CO₂ systems can exceed the envelope of many standard compressed fibre gasket grades. Do not specify from the generic refrigerant listing alone; confirm pressure, temperature, joint design and material compatibility for the exact R744 duty.
- Flange standard and gasket dimension: the correct gasket thickness and outer/inner dimension for the flange standard in use — EN 1514-1, ASME B16.21 (non-metallic flat gaskets) or equivalent.
This article does not constitute a material approval for any specific refrigerant compound. The listing of FLEXSEAL PRO 350 for refrigerants and cooling applications is taken from the material technical data. For critical refrigerant containment applications, the chemical resistance chart for the FLEXSEAL PRO 350 grade should be obtained and reviewed for the refrigerant actually in service, and any regulatory or safety requirements for the refrigerant type should be confirmed independently.
Documentation references for FLEXSEAL PRO 350: DVGW DIN 30653, DVGW DIN 3535-6, EC 1935/2004, FDA 21 CFR 177.2600, FDA 21 CFR 180.22, FDA 21 CFR 181.32, TA-Luft (VDI 2440), WRAS and ZP 5123 are listed as documentation references for the material. These references relate to specific drinking-water, gas, food-contact or emissions requirements for the documented material grade and stated scope. They are not refrigeration-specific approvals. Any refrigeration-specific regulatory requirement must be checked separately against the system design, refrigerant and jurisdiction.
FLEXSEAL PRO 350 is listed for refrigerant media and refrigeration and cooling applications in the Kinetics Line technical data.
Its combination of high compressibility, published leak-rate data and refrigerant media listing makes it a technically appropriate material to assess for compressor flanges, refrigerant pipework and cooling system valves. The specific refrigerant compound should be checked against the FLEXSEAL PRO 350 chemical resistance chart before final specification, particularly for HFO, ammonia or CO₂ systems where material compatibility is more specific.
Practical FAQ
Is FLEXSEAL PRO 350 suitable for refrigerant sealing applications?
FLEXSEAL PRO 350 is a synthetic fibre + NBR binder gasket grade listed for refrigerants, cooling and refrigeration systems among its appropriate application areas. The material data lists compressors and pumps, and refrigeration and cooling, as application categories. For specific refrigerant compatibility — particularly HFC, HFO or ammonia-based systems — the chemical resistance chart for the FLEXSEAL PRO 350 grade should be consulted for the exact refrigerant and compressor lubricant combination in service, as generic refrigerant listing does not cover every individual compound.
What are the operating limits of FLEXSEAL PRO 350 in cooling applications?
The FLEXSEAL source data lists separate maxima of 350°C short-term, 250°C continuous and 100 bar; they are not one simultaneous operating point. It also reports 25% ASTM F36J compressibility and 64% recovery. For refrigeration work, verify the refrigerant-oil combination, combined P-T envelope, face acceptance and required seating stress for the exact joint.
Why does compressibility matter in refrigerant sealing?
Refrigeration and cooling system flanges — particularly on compressors — are often subject to vibration, thermal cycling and lower available bolt loads compared to static piping joints. A higher-compressibility gasket material can help conform to minor face irregularities and maintain sealing contact under these conditions. FLEXSEAL PRO 350 has 25% compressibility and 64% recovery, which may give it more sealing margin on imperfect faces than lower-compressibility fibre grades, provided the media and operating conditions match.