Introduction: Melamine and polyurethane foams both absorb sound, but their polymer chemistry, cellular structure, flame behavior, and temperature limits set them apart in industrial acoustic work.
Walk into any plant with a noise problem and both materials are already there, doing the same job in different places. A flexible polyurethane sheet lines one cabinet, a grey melamine panel lines the next, and on paper both are sold as open-cell acoustic foam. The differences show up when a lining sits inside a duct, a machine guard, or an electrical enclosure where heat, fire requirements, and service life matter as much as the absorption number. The comparison that actually matters sits at the material level: what each foam is made of, how its cells are built, how it behaves near flame and heat, and why engineers keep putting these two side by side for the same acoustic job.
Both foams are open-cell, which means the walls between individual bubbles have ruptured so air can move through the solid skeleton. That shared feature is what makes either one absorb sound instead of reflecting it. Air pushed by a sound wave drags through millions of tiny passages, friction converts part of that motion into heat, and the wave leaves weaker than it arrived. Absorption data published in engineering reference tables shows the same curve shape for porous materials generally: weak at low frequencies, strong through the mid and high bands, and steadily stronger as the material gets thicker. The difference lies in the scale and regularity of the network. Melamine foam is made by foaming a melamine-formaldehyde resin, which produces a very fine, uniform, three-dimensional web with a high share of open cells and a relatively stiff skeleton. A piece feels almost weightless, creases like felt, and springs back without much stretch. Flexible polyurethane foam, built from polyols and isocyanates, usually has larger and less regular cells and a softer, more rubbery skeleton that stretches and recovers. Those structural habits explain a lot of downstream behavior. The fine melamine network packs more surface area and airflow resistance into a thin section, which is why a 50 mm melamine sheet reaches an NRC of 0.85 and an 80 mm sheet reaches 0.9. Polyurethane can hit similar numbers, but it often needs more thickness, a denser grade, or an added facing to get there. Neither result is a free win, because density, cell size, and thickness move the absorption curve in both materials.
Flame behavior is where the two materials separate most sharply, and it is the main reason flame-retardant industrial acoustic work keeps returning to melamine foam. Thermal conductivity and service temperature then set the boundaries of where each foam can realistically be used.
Melamine foam carries its flame resistance inside the polymer itself. The melamine ring is nitrogen-rich, and when the foam meets a flame the surface breaks down into a carbonaceous char layer that shields the material underneath and starves the flame of fuel. Because the skeleton is a thermoset, it does not melt and drip the way many thermoplastics do. That inherent behavior is what sits behind ratings such as UL94-2013 V0, UL94 HF-1, and GB8624-2012 B1 on melamine foam products. Polyurethane works differently. A basic polyurethane is an organic polymer that burns readily, so acoustic grades depend on added or chemically bound flame retardants to slow ignition and spread. Formulation matters enormously here, since the same base foam can behave very differently from one additive package to the next, and combustion instruments such as a cone calorimeter measure that behavior through heat release rate, ignition time, and smoke production rather than a single yes-or-no label. Both materials follow the same principle: performance belongs to the tested formulation and the test method, not to the family name.
Thermally, both are cellular insulators, and the general rule that trapped air does the insulating applies to each. Reported values shift with density, cell structure, and measurement standard, which is why engineering tables list foams as a range rather than one fixed number, and why melamine foam manufacturers usually publish the conductivity figure together with the standard behind it. Melamine foam is documented at a thermal conductivity of ≤ 0.35 W/(m·K) under GB/T10295, alongside an apparent density of 7.00–11.00 kg/m³. The gap opens wider on temperature. Melamine foam is rated from -200 °C to +240 °C, so a lining can sit behind a hot machine housing or along a cold duct run without losing its shape. Common flexible polyurethane acoustic foams are comfortable in a much narrower band and soften or deform well below 240 °C, which is why they tend to appear in room-temperature enclosures instead. That difference shapes specification choices.
Industrial noise control guidance consistently points to absorptive linings inside machine guards, ducts, and cabinets as one of the practical ways to cut noise at the source. That is exactly where the comparison becomes unavoidable, because those linings sit in enclosed, hard-to-reach spaces that are rarely opened for inspection. A duct liner, a control cabinet panel, or a machine housing insert has to keep absorbing sound for years while also surviving the heat of the equipment beside it and meeting the fire requirements attached to the assembly. When one material is easier to install but has to be re-specified or replaced later, the cheaper first order stops being cheap. Melamine foam also brings a combination few single materials offer at once: fine open-cell absorption, thermal insulation, a very wide service temperature, and inherent flame ratings, all in a foam light enough not to load the structure it is bonded to. That combination is why it appears in HVAC ducts, electrical enclosures, and machine housings, and why engineers comparing foams for those spots keep melamine on the short list. For a documented example, Kangerna Melamine Foam lists density, NRC, thermal conductivity, service temperature, and flame ratings in one data set. The honest conclusion is conditional rather than absolute. Polyurethane remains a workable acoustic foam for cooler, less regulated spaces, and melamine is not the automatic answer everywhere. The right question is whether the assembly has to satisfy a flame standard, a temperature extreme, or a long service interval with no easy access. If it does, the material comparison usually narrows on its own.
Melamine foam and polyurethane foam are both open-cell absorbers, and on pure sound absorption the two can land close together. They separate on chemistry and limits: a thermoset melamine network that chars instead of melting, a service range from -200 °C to +240 °C, and flame ratings built into the polymer rather than added to it. Polyurethane stays a reasonable choice for cooler, lightly regulated spaces where its formulation meets the requirements. For ducts, enclosures, and hot machine housings with access problems and fire rules attached, those structural advantages are usually what push the decision toward melamine.
A：Both are open-cell foams, so each absorbs sound through air moving inside a porous network, but the networks are built differently. Melamine foam has a fine, uniform, three-dimensional cell structure with a stiff thermoset skeleton, which packs a lot of airflow resistance into a thin sheet. Flexible polyurethane foam typically has larger, less regular cells and a softer, stretchier skeleton, so it often needs more thickness or higher density to reach comparable absorption.
A：The flame resistance comes from the polymer itself. Melamine is a nitrogen-rich chemistry, and when the foam meets a flame its surface forms a char layer that shields the material below instead of melting and dripping. That behavior supports ratings such as UL94-2013 V0, UL94 HF-1, and GB8624-2012 B1, and it is a real advantage in ducts, cabinets, and machine housings where an acoustic lining is hidden and rarely inspected.
A：Both are cellular insulators, and measured conductivity depends on density, cell structure, and test method, so the fairest comparison uses values taken under the same standard. Melamine foam is documented at ≤ 0.35 W/(m·K) under GB/T10295 with a -200 °C to +240 °C service range. Common flexible polyurethane acoustic foams operate in a much narrower, cooler band and soften well below 240 °C, which limits them to lower-temperature enclosures.
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