SOUND DEADENING, INSULATION, & MOISTURE BARRIER
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Insulation and sound deadening are usually carried out at the same time, and so are often lumped together under a single banner. They include (at least) three distinct layers:
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Mass loading sound deadening - applied directly to the bare metal inside vehicle panels and floor, this layer lessens the noise that the vehicle itself makes. In particular, vibrations, thrumming, and resonance from the vehicle’s panels is reduced.
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As a minimum, this material should be applied to 100% coverage of the rear wheel arches.
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To improve performance, this material can be cut into strips and applied to 20% or more coverage of side panels, inside doors, and elsewhere.
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Thermal insulation and ambient sound deadening - applied on top of the mass loading sound deadening inside vehicle panels, the aim with this set of materials is to reach 100% coverage inside all side panels, the floor, and the ceiling. Like a jacket, if there is an open section cold will enter through it. To reach as close as possible to 100% coverage a few different but complementary materials are used. This layer does a number of important jobs:
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By adhering closed cell foam or similar to the inside of the panels, the temperature of the inner metal is made the same as the outer, preventing condensation from forming.
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Ambient sound, such as the sound of tires on the road surface, other vehicles driving, and sounds of a campsite, is muffled.
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Heat/cold exchange between the outside of the van and the inside is lessened.
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Moisture or vapour barrier - applied over the openings in vehicle panels, under any ply-lining or interior trim. This prevents moisture created by the vehicle’s occupants, such as rain-soaked clothing, cooking, or even breathing, from entering the panel sections, running down internal structures, and corroding the bottom of the vehicle.
All vehicles come from the manufacturer with a small amount of sound deadening applied, usually as foam blocks in the middle of panels. These are designed to cut vibrations while driving and stop the panels from making a thrumming noise but do little to block the road and ambient noise. Panel vans, in particular, have very little sound deadening as standard.
As a general rule of thumb, it is more efficient to use layers of different materials rather than one thicker layer of a single material. This is usually also a more cost-effective approach. The idea is to use different materials which work in different ways to create a “tortuous path” for sound and heat to travel through.
Other Types of Insulation
Residential or industrial insulation, such as loft insulation or similar, must never be used in vehicles. Buildings naturally breathe and don’t condensate much, if at all, so water retention isn’t an issue. Vehicles condensate heavily and water creates corrosion, which will be highly damaging over time and in areas that are difficult or impossible to see. Some popular residential insulations will absorb around 270 times their own volume in water, which will seep down through the material to pool at the bottom, causing corrosion and rot. This is often the source of the musty smell in older campervans and results in the most common repair to their bodywork.