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Polymer vs. Metal Seals: A Comparison In Critical Space Systems

Sealing systems in space applications must perform reliably under demanding conditions in engineering: cryogenic temperatures, vibration, leakage control, ultra-high vacuum, ionizing radiation, abrasive particulates, and repeated thermal cycling. Each factor strains conventional sealing technologies. In combination, they can rapidly cause failure in systems where margins are unforgiving and maintenance is impossible.

As spacecraft architectures evolve toward longer operational lifetimes and broader mission profiles, sealing requirements continue to tighten. Launch vehicles, satellites, and exploration platforms now operate across wider temperature ranges and in contact with more aggressive propellants and media. As a result, both metal seals and engineered polymer alternatives are evaluated—and selected—against increasingly specific, measurable performance criteria.

Over more than 65 years of supporting space programs — from the Apollo missions to Mars Rover Curiosity and the Falcon 9 — Omniseal Solutions has accumulated application data across both polymer and metal sealing technologies. The following is a practical comparison of where each performs, and why.

Conventional Sealing Approaches (Advantages & Limitations)

Three material classes have historically addressed sealing requirements in space applications: elastomer gaskets, metallic seals, and engineered polymer spring-energized seals.

An assortment of polymer seals developed by Omniseal Solutions.

Elastomer gaskets offer compliance and ease of installation but are poorly suited to space environments. Most lose elasticity at low temperatures and degrade at elevatedones. Under vacuum, they outgas volatile compounds that can contaminate optics, sensors, and electronics. Radiation exposure accelerates breakdown further, limiting usable service life in orbital applications.

Metal seals offer mechanical strength, broad temperature capability, and resistance to chemical degradation. However, they require high seating loads and tightly controlled surface finishes to generate sufficient contact stress. In cryogenic environments, differential thermal contraction can reduce contact force and increase leakage risk. In dynamic applications, metal-to-metal contact introduces galling risk and higher actuation forces.

Polymer spring-energized seals were developed specifically to bridge the gap between elastomers and metal. A PTFE or high-performance polymer jacket paired with a metal spring energizer maintains consistent contact pressure across wide temperature and pressure excursions — compensating for thermal shrinkage and creep where a passive design would lose sealing force. The result is a seal that handles cryogenic temperatures, low outgassing requirements, and dynamic interfaces where neither elastomers nor metal alone are practical.

An assortment of metal seals developed by Omniseal.

Engineered Polymer Seals: Operating Principles & Design Architecture

Advanced polymer seals should not be confused with elastomer gaskets. They are precision machined components produced from high performance PTFE, thermoplastics, or polyimides, designed with tight dimensional tolerances and material properties matched to the application environment.

Polymer spring-energized seals operate across a temperature range from approximately −240°C to 280°C (−400°F to 536°F) and can handle pressures up to approximately 1,380 bar (20,000 psi) depending on design. In dynamic applications, the low coefficient of friction of PTFE-based jacket materials significantly reduces actuation torque relative to metal-on-metal contact — an important factor in valve and feedthrough assemblies where torque budget and actuator sizing are constrained.

The wear and friction control of the polymer jacket material reduces torque in dynamic and rotating applications such as valve stems and feedthroughs. This extends service life, a meaningful advantage in mass and power constrained satellite systems.

An assortment of spring-Energized Metal C-seals developed by Omniseal.

From an outgassing standpoint, Omniseal® space-qualified PTFE and Meldin® polyimide grades are formulated to meet the ASTM E595 thresholds — total mass loss (TML) ≤1.0 percent and collected volatile condensable material (CVCM) ≤0.1 percent — that protect adjacent optical and electronic assemblies. PTFE and polyimide compounds also show broad chemical compatibility with the cryogenic propellants most common in launch vehicle service: liquid oxygen, liquid hydrogen, and liquid methane.

Engineered Metal Seals: Operating Principles & Design Architecture

Metal seals are the governing choice when leakage control requirements fall below what polymer permeability can reliably achieve, particularly over multiyear unserviced lifetimes. While polymer seals offer strong performance across a broad range of space applications, metal seals are selected when those solutions have reached their practical limits in terms of temperature, pressure, or required leakage rate — especially in cryogenic or hermetic applications. In precision satellite subsystems with extremely tight leakage requirements, metal seals can meet performance thresholds that polymer solutions cannot.

Meldin® 7001 polyimide components.

Omniseal® metal seals are formed using multi-stage metal forming processes with superalloys selected for the thermal and chemical demands of each application. The portfolio covers C-Seals, spring-energized C-Seals, E-Seals, V-Seals, segmented designs, and metal boss seals conforming to AS5202 fittings. Coatings are a defining feature: standard options include nickel, silver, copper, and gold plating, and Omniseal Solutions has also developed a proprietary wear-resistant coating (NCCM) that migrates to the mating hardware surface, reducing wear on both the seal and the flange — particularly relevant in large-diameter applications where contact uniformity is harder to control.

Omniseal® metal seals cover a temperature range from −269°C to 1,000°C (−452°F to 1,832°F) and pressure performance from vacuum conditions to 6,895 bar (100,000 psi). Metal seals are non-permeable by nature — unlike polymer materials, their impermeability does not depend on material thickness or application-specific permeability coefficients. This makes them the practical solution for hermetic enclosures where leakage performance must be maintained over mission lifetimes measured in decades.

Metal face C-seals.

The case studies below illustrate how polymer and metal sealing solutions are applied across satellite and launch vehicle programs, each driven by distinct industry or regulatory requirements.

Sealing in Satellite Structural & Instrumentation Systems — Matching Solution to Challenge

Satellites carry instrumentation that must operate continuously for years without maintenance, protected from the external space environment and internal corrosive substances such as hypergolic fuels. Across different subsystems within the same platform, the governing sealing requirement varies — and so does the optimal material choice.

Satellites illustrate why seal selection cannot be categorical — different subsystems on the same platform impose different governing requirements, and both material classes are often deployed together.

Structural connectors use Meldin® 7001 polyimide. In primary framework bracket connectors, Meldin® 7001 polyimide replaced metallic and ceramic alternatives. Design priorities were mass reduction, machinability, and electrical and thermal insulation between connected elements — met while maintaining low outgassing performance to protect adjacent assemblies. On the same platform, Omniseal® spring-energized seals in PTFE-based materials handle propulsion valve and tank interfaces where chemical compatibility with hypergolic fuels governs.

Precision instrument enclosures use spring-energized metal C-seals. Where hermetic integrity is required — as in weather satellite calibration instruments — metal is the governing choice. Polymer permeability, including PTFE, cannot meet the long-term leak-rate thresholds needed to protect precision sensors and optics over a multi-year unserviced mission. Spring-energized metal C-seals are specified in these enclosures: silver plating conforms to microscopic surface variations in the mating hardware, while the integrated spring maintains contact stress through differential thermal expansion across the full thermal cycle.

The principle is consistent: structural compliance and chemical resistance favor polymer; hermetic integrity over mission lifetime favors metal — not because polymer is inferior, but because it has reached its permeability limit for that application.

The RACO® Spring-Energized seal.

In precision satellite subsystems — attitude and heading reference systems, laser assemblies, radar electronics, and weather calibration instruments — metal C-seals and boss seals conforming to AS5202 are specified to protect enclosed electronics and optics over the full mission lifetime. Silver-plated sealing surfaces conform to microscopic variations in the mating hardware, while the integrated spring maintains contact stress across thermal cycling, compensating for differential expansion between dissimilar materials. These applications favor metal when the hermetic integrity requirement over 10 to 15 years of unserviced operation cannot be met by polymer alternatives.

The RACO® spring-energized seal was developed specifically to address cryogenic face-sealing challenges encountered in early space programs. Its heavy-duty U-shaped spring maintains sealing force through extreme thermal excursions — a design that has been qualified for use in launch vehicle propulsion systems and has been fielded in the Atlas V, Delta IV, and Falcon 9 programs. RACO® seals are produced in face diameters from 15 to 3,000 mm, with cross-sections from 1.4 to 12.7 mm and minimum tolerances of ±20 μm.

Conclusion

Neither polymer nor metal seals are universally optimal in space applications. Polymer spring-energized seals — including the RACO® design developed for cryogenic space programs — offer the compliance, low friction, and outgassing control needed in propulsion, dynamic, and mass-sensitive applications. Metal seals provide the hermetic integrity and extreme temperature/pressure capability needed in satellite instrumentation enclosures and launch vehicle hot-gas paths where polymer materials have reached their limits.

The most reliable architectures apply each where the application data supports it, validated through testing against the applicable qualification standards. Omniseal Solutions’ combined polymer and metal portfolio — developed across more than six decades of space program participation — supports both paths within a single supplier relationship.

Related technical resources, including a white paper on polymer and metal seal selection in cryogenic space applications, are available through Omniseal Solutions’ technical resource library.

* PFAS-Free here means we do not intentionally add PFAS material in the product, but does not exclude the possibility of traces, as these materials are common in the environment.

Topics:
Adhesives/Sealants Aerospace Materials Metals Polymers

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