Hydrophobic Melamine Foam (HMF)

Absorb

After controlling resonance in your vehicle's panels with CLD Tiles™ and blocking airborne sound with MLV and CCF, our final opportunity to reduce noise levels is absorption.

Hydrophobic Melamine Foam has an extraordinary combination of properties that make it ideal for our application.

Hydrophobic Melamine Foam is sold as 24"x24" (4 ft²) pieces. We have 3/4" and 1.5" thicknesses.

3/4" and 1.5" Hydrophobic Melamine Foam

Absorb

"Melamine Foam was shockingly effective above the headliner and in the pillars."

Jason
Charlotte, NC

The frequencies absorbed by a perfect absorber are determined by the thickness of the absorber. 

Critical concept. The thicker the absorber, the lower the frequency of the sound it will destroy. By destroy I mean converted to miniscule amounts of heat through friction between the air the sound moves and the absorbent medium. I've seen claims that 1/8" CCF is a useful absorber. CCF is a poor absorber but even if it were the best absorber in the world, it would be most effective for sound at or above 27 kHz.

Here's what 27 kHz sounds like. I can't hear it at all.
A 1/4" thick material gets you to 13 kHz. 
3/4" thick, most effective at 4.4 kHz and above. Here's 4.4 kHz:
1.5" gets us to 2.2 kHz and above. Here's 2.2 kHz:

There is a lot of junk sound in this range that is worth cleaning up but it is not a broad spectrum solution. That's why we need MLV and CCF. Looked at another way, to target sound at 250 Hz and above, you'd need an absorber more than a foot thick.

Key reasons an absorber can not be the primary noise reduction treatment in a vehicle:

  1. Insufficient space to install a layer of material thick enough to absorb lower frequencies.
  2. Absorbent materials usually need protection from the elements.
  3. Related to insufficient space, the absorber won't function well if compressed.

Applications:

There are several areas where an absorber can be used effectively. Between the roof and headliner, inside hollow trim panels and to fill voids, like empty quarter panels. Absorbers are the only product in this category that work better the more you add to the passenger compartment air space. 

We used 3M™ Thinsulate™ Acoustic for years with great success. A staggering price increase and changes to the product sent me looking. I really enjoy evaluating and testing new products. It's how I got started in this field in the first place. I love it when I find something great.After working with a few dozen possibilities, I did.

I was intrigued by Melamine foam very early in the process. My first stop at Wikipedia yielded this:

Melamine foam is a foam-like material consisting of a formaldehyde-melamine-sodium bisulfite copolymer.

The foam is manufactured in Germany by BASF under the name "Basotect". It has been used for over twenty years as insulation for pipes and ductwork, and has a long history as a soundproofing material for studios, sound stages, auditoriums, and the like. The low smoke and flame properties of melamine foam prevent it from being a fire hazard.[1]

It is also the component of Magic Eraser and similar cleaning products.

It is also used as the only sound and thermal insulation material for bullet trains, due to its high sound absorption, excellent thermal insulation performance and light weight.

Cool. I was a little concerned about the formaldehyde reference but it turns out not to be an issue at all. Melamine foam meets the most stringent formaldehyde standards in the world.

 

Here's what BASF says their product. 

Melamine foam has a problem for our application that almost knocked it off the list. As manufactured, Melamine foam soaks up moisture like a sponge. The first things I do when looking at any new material for use in vehicles is set a piece on fire and soak a piece it in water. It turns out that a US company takes BASF Melamine foam and treats it using a proprietary process to render the Melamine foam hydrophobic. Water is repelled but air passes through as easily as before and there are no significant changes to any of the material properties we want. 3/4" Melamine Foam is the only product we sell that isn't manufactured in the US but it is modified in the US to meet our requirements.

Why do we care if our absorber is waterproof if we aren't going to be exposing it to the elements? Two reasons. The first is accidental exposure - we don't want a leak or spill to turn 10 ounces of dry absorber into 30 pounds of saturated absorber. We also don't want moisture to create breeding ground for mildew or other organisms that don't belong in our vehicles. 

It's considered acceptable for a material to burn when in direct contct with flame, as long as it extinguishes itself soon after it's removed from the flame. You can see a material that doesn't meet this standard and one that does on the CCF page.

Hydrophobic Melamine does considerably better than that standard. It never really flames, just sort of chars away.

3/4" and 1.5" Hydrophobic Melamine Foam

Specifications

Dimensions 24"x24" (609 mm x 609 mm)
Thickness .75" (19 mm) or 1.5" (38mm)
Application temperature up to 464°F (240°C)
R-Value .75"=3, 1.5"=6, 3"=12
.75" Noise Reduction Coefficient .50
1.5" Noise Reduction Coefficient .77

Working with Hydrophobic Melamine Foam

Products Used

  • Hydrophobic Melamine Foam (HMF)