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PORON, Silicone Foam, Neoprene, or Felt: Selecting Aircraft Vibration Isolation and NVH Materials
Aircraft NVH is really three problems wearing one name: isolating equipment from a vibrating structure, damping the ring out of panels and skins, and blocking airborne sound with mass. The material that wins one job is usually a poor choice for the others, which is why so many isolation parts disappoint. This guide walks the families on the H-O NVH and shock-isolation page, from PORON microcellular urethane to silicone foam, neoprene, felt, cork, and the A2 sound barrier, and matches each to the job it does best.
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Isolation, damping, or a mass barrier: which problem are you solving?
Vibration and noise control fails most often when the wrong tool is chosen for the job, because three different jobs hide under the word "NVH." Isolation puts a soft, resilient element between a vibrating structure and the equipment you want to protect, so motion is not transmitted across it. Damping converts vibration energy in a panel or skin into heat, quieting structure-borne ring and buzz.
A mass barrier adds limp weight to block airborne sound. The material that excels at one is usually mediocre at the others, so the first decision is naming the job, not picking a foam. The families below are sorted by the job they do best.
PORON microcellular urethane: the isolation workhorse
PORON 4701 and 4790 microcellular urethane is the family the avionics world reaches for when an LRU or circuit card has to be isolated in a tight, repeatable footprint. It is prized for low compression set, which means the mount holds its thickness, and therefore its tuning, over years of service rather than flattening into a hard shim. Force-deflection and compression-set behavior are reported per ASTM D3574 on each grade's TDS.
For shock rather than steady vibration, the slow-rebound ShockSeal 4790-79 grade absorbs a transient event and recovers, which is a different property from steady-state isolation.
Silicone foam: the wide-temperature and hot-bay choice
Where a mount sits near a gearbox, a bleed-air run, or in an unconditioned bay, silicone foam holds its resilience across a far wider temperature range than urethane, and several grades carry UL 94 V-0 or HF-1 flammability classes on the TDS. It is the family to name when temperature or a fire requirement, not minimum footprint, drives the choice.
Neoprene and rebonded neoprene: sealing-plus-cushion and economical bulk
Closed-cell neoprene foam (the SCE series) cushions and seals at once, useful where a mount also keeps out moisture or air. For thick, economical cushioning under heavier equipment, rebonded neoprene delivers high load capacity per dollar in pads built up from bonded scrap, with mechanical data per ASTM D1056.
Vinyl nitrile: closed-cell cushion with documented fire behavior
ENSOLITE vinyl nitrile is a closed-cell elastomeric foam that pads, seals, and anti-rattles, with grades whose TDS references the FAR 25.853 interior context. It is a frequent answer for cabin-interior cushioning where a part is a pad first and a fire question second.
SAE pressed felt: damping and broadband absorption
SAE pressed felt is the damping and absorption member of the set: a fibrous material that quiets buzz, squeak, and rattle at sliding interfaces and absorbs broadband noise, available across SAE grades by density. It is the gasket-and-glide material for trim, not a load-bearing isolator.
Cork and cork-wonder pads: high-load equipment isolation
For heavier equipment mounts that need both grip and isolation under sustained load, cork wonder pads combine cork's natural damping with a high load capacity, a long-standing answer under motors, pumps, and ground equipment.
A2 sound barrier: limp mass for airborne noise
When the problem is airborne sound rather than transmitted motion, the BISCO A2 sound barrier adds limp mass with fire-documented silicone chemistry, frequently laminated to a foam decoupler so one converted part both blocks and absorbs.
NVH Families by the Job They Do Best
| Family | Best job | Why it is chosen | Data on TDS |
|---|---|---|---|
| PORON urethane | Isolation | Low compression set; holds tuning over service life; ShockSeal for transients | ASTM D3574 force-deflection, compression set |
| Silicone foam | Isolation, hot/wide temp | Wide temperature range; UL 94 V-0 / HF-1 grades | ASTM D1056; UL 94 class per grade |
| Neoprene / rebonded | Cushion + seal / bulk | Closed-cell seal-and-cushion; rebonded for economical thickness | ASTM D1056 |
| SAE felt | Damping / absorption | Quiets buzz-squeak-rattle; broadband absorption at interfaces | SAE grades by density |
| Cork wonder pads | High-load isolation | Grip plus damping under sustained equipment load | Maker load designations |
| A2 sound barrier | Mass barrier | Limp mass for airborne noise; fire-documented silicone | Areal-mass and fire data per TDS |
Illustrative and relative only; confirm each grade on its current technical data sheet. Job assignments describe common usage, not a substitute for system analysis.
How do fire and temperature reshape the shortlist?
A pad that isolates beautifully at room temperature can be the wrong answer two ways: it can soften and lose tuning in a hot bay, or it can carry no fire documentation for a cabin location. On aircraft, many isolation and trim parts live where the FAR 25.853 interior context applies, so the practical sequence is to name the job, then filter for the temperature range and any fire-documentation requirement, and only then compare resilience and compression set among the survivors.
Silicone foam and the documented vinyl-nitrile grades earn their place precisely because they keep both the mechanical and the documentation boxes checked.
How H-O Products helps
H-O Products die-cuts, waterjet-cuts, laminates, and kits the families above to your drawing in Winsted, Connecticut; we do not manufacture foam or felt in-house. We cut PORON and silicone-foam pads with adhesive backings, laminate barrier-plus-decoupler parts as one piece, build up rebonded pads to thickness, and kit full shipsets of isolation and buzz-squeak-rattle parts to work orders, all under our ISO 9001:2015 certified quality management system with lot-coded traceability and the maker's TDS on the order.
Frequently asked questions
How do I pick an isolation pad for an avionics box or LRU?
Start from the supported mass per mount and the footprint you have, then choose a family for the environment: PORON microcellular urethane for a compact, low-compression-set mount that holds its tuning, silicone foam where temperature or a fire requirement drives the choice. The pad's stiffness and the supported mass together set the mount's natural frequency, so the system behavior, not the material alone, decides whether you isolate; send us the mass and footprint and we will convert to your drawing.
Why did vibration get worse after we added isolation pads?
Almost always because the pad was too stiff for the mass, putting the mount's natural frequency near or above the disturbing frequency, where a mount amplifies instead of isolating. Isolation only begins once the disturbing frequency is well above the mount's natural frequency. A softer grade or more deflection usually fixes it; our companion article on resonance and transmissibility walks through the mechanism in detail.
What is the difference between isolation, damping, and a mass barrier?
Isolation puts a resilient element between a vibrating structure and protected equipment so motion is not transmitted; PORON, silicone foam, and cork serve here. Damping converts panel vibration into heat to quiet structure-borne ring; felt and constrained-layer treatments serve here. A mass barrier adds limp weight to block airborne sound; the A2 barrier serves here. Naming the job first is the whole battle.
Which pad materials survive next to a gearbox or in a hot bay?
Silicone foam holds its resilience across a far wider temperature range than urethane and several grades carry UL 94 V-0 or HF-1 classes, making it the usual hot-bay isolator. Where the part is a cabin cushion with a fire requirement, documented vinyl-nitrile grades referencing the FAR 25.853 context also apply. Confirm the continuous and peak temperature against the grade's TDS.
Can H-O kit a full shipset of isolation and BSR parts?
Yes. We die-cut and waterjet isolation pads, buzz-squeak-rattle felt and foam parts, and laminated barrier assemblies, then slit, back with adhesive, and kit them to your work orders under our ISO 9001:2015 certified quality management system with lot-coded traceability. Send the part list or a sample shipset and we will quote the converted kit.
Get an NVH material recommendation
Tell us the supported mass per mount, the footprint and thickness you have, the environment (temperature, fluids, fire requirement), and whether you are fighting transmitted vibration, panel ring, or airborne noise, and we will recommend a family and quote converted parts.
Samples typically ship in 3 to 5 business days for common die-cut configurations on materials we keep on hand; standard production runs about two weeks after drawing approval; expedited service is available. MOQ varies by material and part.
Family-owned in Winsted, Connecticut since 1971 · ISO 9001:2015 certified · OEMs worldwide send us a drawing — and get back their part.
Related reading
Request a quote for your aircraft vibration & shock isolation part
Send H-O your drawing or describe the part—engineering reviews every RFQ and converts samples on your geometry.
Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
References
- ASTM D3574 (flexible cellular urethane, force-deflection and compression set); ASTM D1056 (flexible cellular rubber); ASTM D395 (compression set); ASTM D2632 (resilience); ASTM C423 (acoustic absorption).
- MIL-STD-810 and RTCA DO-160 (environmental and vibration test methods); SAE AS8049 (seat systems); FAR 25.853 (interior flammability context); UL 94 (flammability classes). Cited by designation; H-O performs no testing.
- Manufacturer technical data sheets: PORON 4701 / 4790 microcellular urethane and ShockSeal, silicone foam, neoprene and rebonded neoprene, ENSOLITE vinyl nitrile, SAE pressed felt, cork wonder pads, BISCO A2 sound barrier.
This article summarizes vibration-isolation and NVH material-selection principles using the families and method designations cited on the parent application page. Comparisons are qualitative; mechanical values are per each grade's current technical data sheet, and no test results are quoted.
Test standards such as MIL-STD-810 and RTCA DO-160 are named by designation for orientation only; H-O performs no qualification testing and makes no airworthiness determinations. All parts are custom manufactured to order; minimum production run quantities vary by material and part. H-O is a converter, not a raw-material producer.