Saint-Gobain’s Norseal® silicone foams are widely used in demanding applications because they balance thermal stability, flame performance, weather resistance, and durability. Among the lineup, F-12, F-15, and F-20 cover a useful span of compliance, firmness, and environmental sealing performance.
In this blog, we’ll compare the three grades, highlight their differences and strengths, and help you choose which one is right for your gasket or sealing application.
What All Three Share in Common
All of these Norseal silicone foam grades offer:
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A very broad operating temperature range (from about –60 °F to +400 °F).
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Flame-retardant behavior and low smoke / low toxicity performance.
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Excellent compression set resistance, meaning they recover after being compressed over time.
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Good resistance to UV, ozone, moisture, and outdoor exposure.
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Conversion flexibility (die-cutting, roll stock, adhesive backing, etc.).
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Use in sectors like aerospace, transit, electronics, lighting, and enclosures.
Because of these shared strengths, the real choice among them comes down to how soft vs. firm you need, how tight the fire/smoke/toxicity constraints are, and whether you need extra environmental sealing (like for water or dust).
F-12 — The Soft, Fire-Blocking Silicone Foam
Profile & Features
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Very low density (light, conformable) with a modified cell structure.
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Combines flame retardancy, low smoke/toxicity, good compression set, and high conformity.
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One side typically textured, the other smooth (though dual-smooth can be custom).
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Meets strict fire standards, including FAR 25.856 (A-1 & B).
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Good for radiant heat shields, fire-blocking gasketing, and lightweight applications.
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Standard thicknesses range from ~0.063 in (1.6 mm) up to 1.0 in (25.4 mm).
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Often supplied in 36″ wide rolls.
Typical Uses
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Fire/heat-resistant gaskets, insulation blankets, radiant heat shields.
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Gasketing in transit, aerospace interiors, or architectural areas where fire safety and low weight are critical.
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Lighting/lamps needing outdoor exposure combined with fire safety.
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Applications where extremely low clamp force is needed or where parts cannot tolerate stiff seals.
When F-12 Is Best
Choose F-12 when you need maximum softness, conformity, and fire performance—especially where clamp force is limited or surfaces are irregular.
F-15 — The “Middle Ground” Silicone Foam
Profile & Features
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A soft to medium-low density foam, more robust than F-12 but still flexible.
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Designed for sealing, cushioning, gasketing tasks that demand non-toxic, low smoke, low flame spread materials.
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Smooth on both sides in standard form.
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Better edge stability and handling than F-12, while still offering good compliance.
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Suitable for both indoor and outdoor use because of environmental resilience.
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Available in more limited thickness choices (smaller range than F-12).
Typical Uses
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Seals for electronics enclosures, LED or lighting fixtures, battery pack cushioning, transit gasketing, etc.
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Where F-12 is too soft and F-20 would be overkill.
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Enclosures needing consistent sealing under moderate loads.
When F-15 Is Best
Pick F-15 when you’re in between: you want more structural integrity than F-12, but want to retain a degree of softness and compliance. It’s the go-to when F-12 is too weak but F-20 is too stiff or heavy.
F-20 — The More Rigid, High-Performance Foam
Profile & Features
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Medium density, closed-cell foam (versus more open/modified structure in F-12 and F-15).
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Smooth surfaces on both sides.
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Strong fire, smoke, toxicity credentials: FAR 25.853, UL 94 V-0, SMP 800-C, etc.
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Excellent compression set and higher compression deflection (i.e. it resists collapsing more under load).
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Offers better environmental sealing (water, dust) than softer open-cell foams.
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Standard thicknesses include 0.031″, 0.063″, 0.125″, 0.188″, 0.25″, 0.375″, and 0.50″.
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Typically supplied in 36″ roll width.
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For EV / battery pack usage, F-20 is often specified for its water-sealing and higher stiffness.
Typical Uses
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Critical aerospace and transit gasketing where fire/smoke specs are intolerant.
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Mass transit, rail, aerospace, military, and demanding electronics.
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Battery pack sealing and EV thermal management (because of better sealing and structural behavior).
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Applications where water sealing, durability, and structural stability are necessary.
When F-20 Is Best
Choose F-20 when you need less compression, more durability, better resistance to collapsing, or stronger environmental sealing (dust, moisture). It’s ideal where a stiffer, more robust foam is acceptable.
Side-by-Side Comparison
| Property / Feature | F-12 | F-15 | F-20 |
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| Density / firmness | Very soft / low density | Soft to medium-low | Medium density, firmer |
| Cell structure | Modified / more open | Intermediate | Closed-cell, fine structure |
| Surface finish | One smooth, one textured (dual-smooth optional) | Smooth both sides | Smooth both sides |
| Compression deflection / stiffness | Low (very compliant) | Moderate | Higher (more resistance under load) |
| Compression set resilience | Very good | Good | Excellent |
| Fire / smoke / toxicity | Meets strict FAR 25.856 A/B & UL 94 V-0 | Meets UL 94 V-0, FAR 25.853 | Meets UL 94 V-0, FAR 25.853, SMP 800-C, etc. |
| Environmental sealing | Good, but open cell / more permeable | Better | Best, closed cell, better water/dust sealing |
| Typical thickness ranges | Up to ~1.0 in | More limited (thinner side) | Up to ~0.50 in common, can handle mid-thick |
| Best for | Ultra soft fire-blocking, low clamp load, irregular surfaces | Balanced gasketing where F-12 is too soft | Stiffer seals, structural, water-resistant, robust environments |
How to Choose the Best One (Design Guidance)
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Clamp Force & Compression Budget
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If clamp load is light or you want minimal stress on mating surfaces, go softer (F-12 or F-15).
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If you have stronger clamp force and need more rigidity or less squish, F-20 may be appropriate.
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Fire / Smoke / Toxicity Requirements
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If your spec demands FAR 25.856, F-12 might be required.
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For typical UL/FAA/FST specs (FAR 25.853, UL 94 V-0, SMP 800-C), F-15 and F-20 are strong choices.
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Sealing & Environmental Requirements
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For best resistance to moisture ingress, dust, or water, the closed-cell nature of F-20 is an advantage.
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For lighter sealing or where water isn’t critical, F-12 or F-15 may be sufficient.
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Durability & Cycle Life
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F-20 resists collapse and handles repeated cycling better in many cases.
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But if excessive stiffness is problematic in your design (risk of cracking or misalignment), softer grades may last better.
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Surface Regularity & Conformability
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For uneven or warped mating surfaces, softer foams (F-12, F-15) provide better conformity.
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If surfaces are well-machined and flat, F-20 can perform well.
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Adhesive & Converting Considerations
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All grades support adhesive backing (PSA) and conversion (die-cut, waterjet, lamination).
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But ensure the PSA choice (acrylic vs silicone) fits substrate and temperature requirements.
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Final Thoughts/More Information
Norseal’s F-12, F-15, and F-20 silicone foams together span a spectrum from ultra-conformable fire-blocking seal to more robust, closed-cell, high-durability gasket material. Each has a place. The trick is matching softness vs. structural requirement, fire/spec constraints, and environmental demands.
If you’re designing a gasket or seal using one of these materials, we can help:
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Pick the right foam grade based on your spec
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Determine ideal thickness, compression levels, and tolerance
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Suggest the correct PSA or backing
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Prototype & convert to your print
Send me your drawing, material, and environment specs, and I’ll help choose between F-12, F-15, or F-20 — or even combine them in laminate constructions if that’s optimal.