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Rebonded Neoprene, Cork, Bearing Pads, or PORON: Choosing Vibration Isolation and Acoustic Materials
A relay armature and a power transformer are both vibration problems, five orders of magnitude apart, and that is the organizing fact of this estate: the load band, how much weight sits on how much pad area, picks the material set before any other property matters.
The H-O vibration, shock, and acoustic control application page spans grams to tons with two distinct material sets plus an acoustic pair, and this guide walks them by the decision each one wins, with methods named by designation: ASTM D1056 for cellular compression-deflection grades, ASTM D3574 for polyurethane foams, ASTM D2240 for solid durometer, ASTM D395 for compression set, ASTM D2632 for resilience, and the UL 94 and FST data lines where rooms and classed assemblies demand them.
Values are per the TDS on file for each grade.
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The heavy band: tons on pads, for decades
Rebonded neoprene: the classic transformer base pad
A transformer hums at twice line frequency, and that hum walks through a rigid mount into the building steel where it amplifies into a tonal complaint. Rebonded neoprene (25# and 27# densities per ASTM D1056 testing on the TDS) is the classic base pad: dense, economical, and stable under tons, developing useful deflection only under serious stress, which is exactly what the heavy band wants.
Rubberized cork: the creep-resistance specialist
Rubberized cork brings cork's natural resistance to long-term flow, tested per the ASTM F36 / F146 gasket-material methods on its TDS. A transformer pad is loaded on commissioning day and stays loaded for thirty years; cork composites are chosen for exactly that duty, with the caveat that they stay indoors.
Atlas bearing neoprene and natural rubber: the engineered ends
Atlas bearing neoprene is engineered structural bearing-pad material with ozone testing per ASTM D1149 and low-temperature testing per ASTM D2137 on its TDS, for bearing duty where the pad is part of the structure. Natural rubber gives the liveliest isolation, with blast grades for impact and defense installations, but wants protection from ozone and oil.
ENSOLITE vinyl nitrile foam covers lighter components with closed-cell consistency, UL 94 HF-1 classes on several grades per TDS, and FAR 25.853 flammability data reported in the TDS family.
The light band: grams to kilograms, precisely
PORON industrial polyurethanes: precision cushioning
Relay armatures chatter when panel vibration reaches them; contactors slam on every operation; boards and displays need cushioning against both.
The PORON industrial line (the 4701 series, very soft through very firm per ASTM D3574, plus extra-soft slow-rebound and sealing shock grades in the 4790 series) holds tight thickness tolerance and resists compression set, which is why one family covers gasket-adjacent cushioning, anti-rattle pads, and shock mounts.
Several grades carry IEC 60093 resistivity and UL 94 listings per their TDS, including a V-0-classed member of the 4701 series for cushioning inside classed assemblies.
HyPUR-cel and hybrid PU: the density ladder
The HyPUR-cel cellular urethane line (I, R, S, T, and V series per ASTM D1056 / D3574 / D2632 testing on the TDS) extends the density map when the duty sits between PORON grades, and the 1.3# hybrid PU foam blends ester-like toughness with ether-like hydrolysis behavior per its TDS for compression interfaces that need a tougher skin than felt.
Felt, cork, and thin PORON: the buzz-and-rattle kit
The cheapest noise to fix is the one that never starts.
Sheet-metal panels buzz against their frames at fastener points, edge overlaps, and harness touch points, a contact problem solved by interposing a thin compliant layer exactly where the metal meets. SAE pressed felt (eleven grades, F-1 through F-55, per ASTM D2475 / D461 on the TDS) is the legacy interface liner that wipes, slides, and silences; thin-gauge PORON die-cuts into washers, strips, and frames; and plain and rubberized cork pad the larger contact patches.
These parts are small, numerous, and high piece-count per assembly, exactly the economics kiss-cut-on-liner die-cutting is built for.
The acoustic pair: absorb and block
Airborne noise control is two different physical jobs that get confused into one purchase order. Absorption turns sound energy into heat inside an open-cell structure: reticulated polyurethane foam (10 through 80 PPI, uncoated, acrylic-, or PVC-coated, with UL 94 HF-1 flame-rated versions per TDS) and polyether PU foam line enclosure interiors and baffle openings.
Blocking stops transmission with limp mass: the A2 sound barrier is a mass-loaded silicone sheet, plain or fiberglass-reinforced, whose TDS reports FAR 25.853-type flammability data. Real enclosure treatments laminate the two, absorber face on barrier layer, die-cut as one part with PSA for assembly.
Isolation & Acoustic Families by Load Band and Job
| Family | Load band / job | Signature property | Typical role |
|---|---|---|---|
| Rebonded neoprene | Heavy (tons) | Dense, stable under sustained load | Transformer and reactor base pads |
| Rubberized cork | Heavy | Natural creep resistance (F36 / F146 methods) | Bases and machine feet, indoors |
| Atlas bearing neoprene | Heavy / structural | Ozone (D1149) and low-temperature (D2137) data | Engineered bearing pads |
| PORON industrial | Light (grams to kg) | Tight tolerance, low compression set | Relay, contactor, and electronics cushioning |
| HyPUR-cel series | Light to medium | Density ladder per D1056 / D3574 / D2632 | Between-grade cushioning duties |
| SAE pressed felt / cork | Contact interfaces | Wipes, slides, silences (D2475 / D461) | Buzz and rattle washers, strips, liners |
| Reticulated / polyether PU | Acoustic: absorb | Open-cell, 10 to 80 PPI; HF-1 versions per TDS | Enclosure linings, baffles |
| A2 sound barrier | Acoustic: block | Limp mass-loaded silicone; FAR 25.853-type data | Transmission loss in equipment rooms |
Illustrative and relative only; confirm each grade on its current technical data sheet. A pad outside its load band either transmits rigidly or crushes flat; the load band picks the set before any catalog page is opened.
Firmness follows the load, never the hand
Divide the supported weight by the pad footprint you have room for, and the answer sorts the family before any other property. Then pick the compression-deflection grade so the operating point sits in the grade's working window: too hard and the pad transmits; too soft and it bottoms out and transmits anyway. Specify solids by Shore A per ASTM D2240 and cellular materials by their ASTM D1056 or D3574 compression-deflection grade; the two metrics do not convert, and "40 durometer foam" is a category error procurement cannot fill.
For any pad under sustained load, read the compression-set line (ASTM D395 and the D1056 suffix methods) before the firmness line.
How H-O Products helps
H-O Products die-cuts and converts sheet, roll, and bun materials; we do not mold isolation mounts. We convert rebonded neoprene, cork, bearing pad stock, PORON, HyPUR-cel, felt, reticulated foam, and barrier sheet to your drawing: base pads cut to the footprint, anti-rattle washers and strips kiss-cut on liner for line application, absorber-on-barrier acoustic laminations supplied as one part, with material traceability and lot-code TDS records under our ISO 9001:2015 certified quality management system in Winsted, Connecticut.
Send the supported mass and footprint with the drawing, and engineering checks the operating point against the family's TDS curve rather than guessing from durometer feel.
Frequently asked questions
What pad material goes under a transformer to stop the hum?
Start with the load band: rebonded neoprene (25# / 27# densities) is the classic transformer base pad, dense and stable under tons, with rubberized cork where long-term creep resistance is the priority and the Atlas bearing line where the pad is structural. The pad isolates by deflecting under load, so the firmness grade per ASTM D1056 is sized so the operating point sits mid-window at your load per area, and the set lines per ASTM D395 are read before the firmness line.
PORON vs HyPUR-cel: how do I choose between them?
Both are precision microcellular polyurethanes graded per ASTM D3574 / D1056. The PORON industrial line is the precision standard, very soft through very firm with tight thickness tolerance and low compression set, plus slow-rebound and shock grades and a V-0-classed member per TDS. The HyPUR-cel series extends the density map when the duty sits between PORON grades. Specify by compression-deflection grade and thickness at your load, not by feel.
What is the difference between sound absorption and sound blocking?
Two mechanisms, two materials. Absorption converts sound to heat inside an open-cell structure, the job of reticulated PU (10 to 80 PPI, with HF-1 flame-rated versions per TDS) and polyether foams, effective on the reflective build-up inside enclosures. Blocking stops transmission with limp, heavy, decoupled mass, the job of the mass-loaded A2 silicone barrier, plain or fiberglass-reinforced. An absorber alone will not stop sound passing through a panel; most real treatments laminate both as one die-cut part.
Which acoustic and cushioning materials carry flammability data on the TDS?
Per the parent page: several ENSOLITE vinyl nitrile grades carry UL 94 HF-1 classes and the ENSOLITE TDS family reports FAR 25.853 data; the 4701 series includes a V-0-classed grade; the reticulated foam line offers UL 94 HF-1 flame-rated versions; the 2# polyether grade reports HF-1; and the A2 sound barrier TDS reports FAR 25.853-type data. The class belongs to the specific grade, so name it on the drawing and keep the TDS with the order file.
Get an isolation or acoustic material recommendation
Tell us the equipment, the supported mass and pad footprint, the mounting, the environment, and any flammability class, and we will recommend a family and firmness direction and quote die-cut parts to your drawing.
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
ApplicationVibration, Shock & Acoustic ControlRead → Sub-applicationHVAC Vibration & Acoustic ControlRead →
GuideWhy Isolation Pads Stop Working: Load Band, Deflection Window, Creep, and the Durometer TrapRead →
GuideHow to Spec Vibration Isolation and Acoustic Parts: What to Send H-O for a QuoteRead →
IndustryElectromechanical & Switchgear hubRead →
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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 D1056 (flexible cellular rubber, compression-deflection grades) and ASTM D3574 (flexible cellular polyurethane methods); ASTM D2240 (durometer, solids).
- ASTM D395 (compression set); ASTM D2632 (resilience by rebound); ASTM D2475 / D461 (wool felt); ASTM D1149 (ozone) and ASTM D2137 (low temperature) on the bearing-pad TDS.
- UL 94 (flammability classes, per grade); ASTM E662 / E162 and FAR 25.853 (FST and flammability data as reported on the ENSOLITE and A2 TDS).
- Manufacturer technical data sheets for the rebonded neoprene, cork, bearing pad, vinyl nitrile, PORON, HyPUR-cel, felt, reticulated foam, and sound-barrier grades named on the parent application page.
This article summarizes vibration, shock, and acoustic material-selection principles using the families and published methods cited on the parent application page. Comparisons are qualitative compression-deflection reasoning; no numeric isolation prediction is made for any design, and per-grade values must be confirmed on the manufacturer's current technical data sheet.
All parts are custom manufactured to order; minimum production run quantities vary by material and part. H-O is a die-cut converter, not a raw-material producer, and does not mold isolation mounts.