Permeation and Outgassing in Seals: Designing for Vacuum, High-Purity Gases, and Solvents
Updated: Sep 22, 2025
Introduction
Seals in advanced industries face challenges that go far beyond temperature and chemical exposure. Two of the most subtle but consequential issues are permeation and outgassing. Both phenomena undermine sealing integrity, system cleanliness, and long-term reliability.
- Permeation is the diffusion of gases or liquids through the seal material, leading to leaks or cross-contamination.
- Outgassing is the release of volatile substances from within the polymer itself, contaminating sensitive environments.
While these effects can seem invisible, their consequences are severe: vacuum chambers that never reach target pressure, semiconductor wafers contaminated by microscopic films, aerospace fuel systems that lose efficiency, or medical production lines compromised by trace residues.
This article provides a comprehensive technical overview of permeation and outgassing, material comparisons across polymer families, industry-specific considerations, and design strategies to minimize risk. Get in touch with the Canyon Engineering team now!
The Science of Permeation
Diffusion and Solubility
Permeation is governed by two linked processes: diffusion (movement of molecules through the polymer network) and solubility (the degree to which the gas or liquid dissolves into the elastomer). The overall permeability coefficient is the product of both.
- Polymers with dense, fluorinated backbones (e.g., FKM, FFKM) limit diffusion by restricting free volume.
- Materials with open chain structures (e.g., silicone) allow much higher rates of diffusion.
- Solubility depends on the polarity and size of the penetrating molecule: hydrogen and helium diffuse rapidly, while larger hydrocarbons are slower. Get in touch with the Canyon Engineering team now!
Factors Affecting Permeation
- Temperature: As temperature increases, polymer chain mobility rises, accelerating diffusion.
- Pressure gradients: Larger differentials drive faster permeation rates.
- Cross-section: Thicker seals slow permeation but cannot stop it entirely.
- Media compatibility: Swelling from chemical exposure increases free volume and permeability.
Real-World Impacts
- In vacuum systems, permeation of atmospheric gases can prevent reaching ultra-high vacuum levels.
- In automotive fuel systems, permeation leads to fuel odor emissions even without visible leaks.
- In aerospace, oxygen permeation raises fire safety concerns.
The Science of Outgassing
Outgassing is distinct from permeation. Instead of external molecules moving through the polymer, outgassing originates from volatile substances within the elastomer itself.
Sources of Outgassing
- Residual monomers and oligomers from polymerization.
- Plasticizers, curing agents, and stabilizers added during compounding.
- Absorbed environmental gases or solvents retained in the material during storage.
Triggers for Outgassing
- Vacuum conditions: Low pressure accelerates the release of entrapped volatiles.
- Heat: Elevated temperatures mobilize additives and low-molecular-weight fractions.
- Radiation and plasma exposure: Breaks down polymer chains, creating volatile byproducts.
Consequences
- Contamination: Outgassed molecules deposit on optics, wafers, or medical products.
- Reduced performance: Mass spectrometry, electron microscopy, and aerospace sensors can be compromised by even trace contamination.
- Extended pump-down times: Volatile release slows vacuum chamber preparation. Get in touch with the Canyon Engineering team now!
Material Comparisons
Different polymer families exhibit distinct permeation and outgassing behaviors. Selecting the right elastomer is the most powerful lever for controlling these risks.
|
Polymer Family |
Permeability / Outgassing Behavior |
Notes & Applications |
|
Butyl (IIR) |
Very low permeability; excellent gas barrier |
Often used in vacuum and inflatable systems. Limited
rebound speed and narrower chemical resistance window. |
|
Nitrile (NBR) |
Moderate permeability; good oil and fuel resistance |
Common in hydraulic and fuel systems but not suitable for
ultra-clean environments. |
|
Hydrogenated Nitrile (HNBR) |
Lower permeability than NBR; good resistance to heat and
oxidation |
Aerospace hydraulics and refrigerant service. Less common
in vacuum. |
|
Silicone (VMQ, PVMQ) |
High permeability; poor barrier performance |
Excellent for extreme low temperatures; poor choice for
vacuum sealing. |
|
Fluorosilicone (FVMQ) |
Better fuel resistance than silicone, but higher
permeation than FKM |
Aerospace fuel handling and low-temp flexibility. |
|
Fluorocarbon (FKM, Viton®) |
Excellent chemical resistance; low permeation |
Industry standard for aerospace, automotive, and chemical
processing. |
|
Perfluoroelastomer (FFKM, Canrez®, Kalrez®) |
Low permeation and outgassing |
Semiconductor fabs, plasma chambers, pharma cleanrooms,
space applications. |
|
Aflas® (TFE/P) |
Excellent resistance to steam, amines, and caustics |
Oil & gas, power generation, and chemical processing.
Moderate gas permeability. |
|
PTFE and PTFE Spring-Energized Seals |
Near-zero permeability; negligible outgassing |
Ideal for ultra-high vacuum, cryogenic sealing, and
aggressive chemical solvents. |
Expanded Design Strategies
Material Selection Beyond Basics
Choosing the right polymer family is the first step. For example:
- Semiconductor: FFKM grades with low metal ion content are required to prevent wafer contamination.
- Vacuum research: PTFE and spring-energized designs minimize permeation and ensure long-term stability.
- Chemical reactors: AFLAS compounds withstand aggressive amines and steam.
Groove and Hardware Design
- Tight gland tolerances reduce seal deformation and lower permeation paths.
- Backup rings prevent extrusion, allowing use of softer low-permeability materials.
- Dual-seal designs with vented interspaces can capture permeation and prevent contamination.
Surface Treatments
- Plasma nano-coatings reduce absorption and surface reactivity.
- Parylene coatings improve barrier performance and reduce extractables.
- Surface fluorination creates a denser outer layer that slows gas uptake.
Preconditioning and Bake-Out
Seals for vacuum service should be pre-baked to remove volatiles before installation. This is standard in semiconductor fabs, space hardware, and laboratory systems. Get in touch with Canyon Components for pre-vacuum baked parts.
Maintenance and Predictive Replacement
Permeation and outgassing are time-dependent. Predictive replacement schedules based on historical data reduce the risk of unplanned downtime. Get in touch with the Canyon Engineering team now!
Industry Applications
Semiconductor fabs require ultra-clean, vacuum-tight seals. Plasma etch and deposition chambers use FFKM compounds that combine chemical resistance with low outgassing. PTFE spring-energized seals are used in wafer handling and load-lock chambers where ultra-high vacuum must be preserved. Get in touch with the Canyon Engineering team now!
In aviation, permeation-resistant materials like FKM and FVMQ prevent fuel vapor loss. In spacecraft, outgassing is a mission-critical issue: contaminants can coat optics or interfere with sensors. NASA and ESA both require seals to meet stringent outgassing specifications. FFKM and PTFE dominate in these applications.
Chemical Processing and Energy
Processing plants expose seals to solvents, caustics, and hydrocarbons under pressure and heat. FKM is often the first choice, while AFLAS provides resistance to steam and amines. For extreme chemical compatibility, perfluoroelastomers provide unmatched protection.
Cleanroom environments cannot tolerate molecular contamination. Outgassing from seals can jeopardize sterility and product safety. USP Class VI and ISO 10993-certified FFKM materials are standard, while PTFE seals provide additional barrier protection in drug production and sterile filling.
Spectroscopy, mass spectrometry, and particle accelerators require seals with ultra-low permeation. Butyl rubber provides a low-cost option for moderate vacuum, while FFKM and PTFE are sometimes necessary for ultra-high vacuum.
Expanded Case Studies
Case 1: Plasma Etch Chamber (Semiconductor)
A manufacturer of advanced chips experienced rapid seal failure in plasma etch chambers. Standard FKMs degraded due to fluorine plasma exposure and released contaminants. By switching to a Canrez® FFKM with ultra-low particle generation, seal life increased threefold and wafer yields improved.
Case 2: Satellite Optics (Aerospace)
Outgassing from elastomer seals in optical housings caused fogging of space telescope lenses. Transitioning to PTFE spring-energized seals eliminated the problem, ensuring mission reliability.
Case 3: Chemical Reactor (Industrial Processing)
An amine-based chemical process experienced rapid permeation through conventional FKMs. AFLAS seals were adopted due to superior amine resistance and longer service intervals, cutting downtime by 40%.
Case 4: Sterile Filling Line (Pharmaceutical)
A medical device company found silicone seals releasing volatiles that compromised sterility. Switching to USP Class VI FFKM eliminated outgassing, meeting FDA and EMA compliance while maintaining product purity. Get in touch with the Canyon Engineering team now!
Conclusion
Permeation and outgassing are subtle but decisive in determining seal performance. Whether in semiconductor cleanrooms, chemical reactors, aerospace fuel tanks, or medical production lines, the choice of material dictates reliability and safety.
- Vacuum Baking most elastomeric materials results in significantly less outgassing.
- Butyl offers cost-effective vacuum performance.
- FKM provides all-around resistance in aerospace and processing.
- FFKM sets the standard for ultra-purity and vacuum.
- PTFE seals achieve near-zero permeation and outgassing.
By combining advanced materials with thoughtful design strategies, Canyon Components delivers sealing solutions that meet the highest industry demands.
