Car Soundproofing: The Complete Guide to Mass-Loaded Vinyl

Reducing excessive noises coming into the cabin, and vibrations through the steering wheel, seats, armrests and the floor is one of the main ways to improve driving comfort and combat distractions and fatigue. Car brands are now doing more to lessen NVH (noise, vibration, harshness) levels with innovative products based around soundproofing materials, and design solutions (inverter electric motors, improved aerodynamics, revised tyre treads, and better all-round build) for whisper-quiet interiors. Even cars in basic trims now compare to luxury vehicles of just a few years ago in terms of how quiet they are. And it’s luxury cars where soundproofing started. 

To deal with the range of noises distracting you while driving (tyre, wind, road, engine, transmission, exhaust etc) and becoming a safety hazard, varied soundproofing and sound-deadening products are used. Older vehicles used bitumen-based acoustic layers that happily absorbed sounds until heat and general wear caused crumbling and wrinkling. This left exposed areas where sound got through.

Newer products are combined to improve sound absorption and block sound waves from reaching the interior. Apart from thinner, pressure-sensitive butyl rubber layers lining the most critical parts, an additional loaded vinyl soundproofing layer helps block out remnant sounds eagerly vying for your attention. The material is also known as Mass Loaded Vinyl (MLV), and is dense and heavy enough to deal with louder sounds. 

Basics of Mass Loaded Vinyl in Car Soundproofing

Mass-loaded vinyl is an industry-standard acoustic barrier. It is a dense, thin and flexible material, made of PVC sheet and loaded with barium or calcium silicate to add weight. It is recognisable by its black or dark grey colour. The material has been used for decades in construction, and now in automotive soundproofing. 

MLV works by blocking sound waves. This is enabled by its density and the mass added to attached car parts by the mineral filler. And since it is limp it doesn’t vibrate, or pass on energy to surrounding vehicle components. Weight starts at 4 kilos per square metre and can be sourced in various thicknesses, ranging from 2 to 5mm (depending on the available space). The added mass to parts like floors, firewalls and boots effectively reduces engine, transmission and exhaust noise. Soundproofing and effectiveness can be further increased by using a higher filler content, with the MLV layer remaining relatively thin and working in most vehicle areas. Or by going with several stacked layers, or larger thicknesses where possible. If you’re worried about airborne noises, such as that from tyres, wind and passing traffic, MLV can drone this out too when installed correctly. 

Where It’s Used

Areas like floor pans, front and rear firewalls, wheel arches and rear car seats are where MLV can really shine.  As mentioned, the material works best when combined with a butyl base layer that acts as the first line of defence, before the weight of the loaded vinyl soundproofing mat smothers remnant noises, and prevents vibrations or resonance. 
The material is ideal for car rebuilds, in performance mods for more power (and hence noise), and vehicles that tend to see heavy use on less-than-perfect roads. This includes new and old 4WDs, utes, vans, trucks and station wagons. Mass-loaded vinyl can adequately limit engine noise in bigger displacement cars as well as older inline 6s, V8s and flat-four engines. It also prevents vibrations from reaching the cabin, and to an extent acts as a heat barrier, by lowering temperatures from hot engine, transmission and exhaust parts. 

Installing MLV is simple. While the material can be used independently, the best soundproofing results are achieved with a multilayered approach. First is the butyl layer, cut to size and shape, followed by an insulative foam decoupler, with the thin mass-loaded vinyl roll blocking remnant noise. The material is easily cut with a utility knife. Ensure you measure each piece, and that there are no exposed areas where sound can escape. Pieces can be removed at will, but if you need a permanent solution, spray the backing with an adhesive. 

Benefits of MLV in Car Soundproofing

Luxury brands have used thicker MLV sheets for ages and to good effect. The material is pliable, easy to work with and capable of drowning out the loudest sounds. Consider mass-loaded vinyl sound insulation if you need: 

• Unrivalled soundproofing – when done right, MLV reduces airborne and structural noise from distracting you while driving. The material is used in firewalls, floor pans, wheel arches and boots (among other areas) to smother vehicle and ambient sound. You can enjoy your favourite tunes without cranking up the volume, and have a decent conversation in a whisper-quiet cabin. 
• Slim profile – at a few millimetres thick, MLV fits in tighter spaces even when combined with thicker layers in other materials. This allows use across many types of vehicles. 
• Easy and quick installation – you won’t need a degree or apprenticeship to install MLV. The material comes in set roll sizes (around 1350 by 2000mm), is easy to shape and cut, and is even easier to fit in the intended vehicle area. A quick swirl of adhesive spray keeps pieces in place, without the risk of slippage. 
• Versatility – soundproof vinyl layers are good for a range of cars. The material also blocks heat and besides cars, excess material can be repurposed for soundproofing in caravans, garages, homes and other areas. 
• Value for money – low purchase price and the fact that you can skip high installation costs make MLV good value.