Sound Deadening & Thermal Insulation Advice

No. Two or three layers of different materials give the best result, because each one deals with a different kind of noise. But all three layers aren’t practical in every vehicle or every panel. On one van door, for example, there wasn’t room for ST-Mat over the mat on the metal partition, so we left it out. See Soundproofing Basics.

No. Covering at least 50% of each panel gives a noticeable result. Start in the centre of the largest flat areas and use the knock test: tap the panel, and add mat until it sounds dull instead of hollow. What matters more is that every piece is rolled down firmly with a metal roller, with no air pockets.

1.5mm is the lightest, for doors, roof and bonnet. 2mm is the all-round mat for roofs, doors and van side panels. 3mm and 4mm are for floors, wheel arches and the bulkhead, where most road noise comes in. Thicker mats damp more but add weight.

Usually not, but knock-test any large flat areas (often around the wheel arches) and put mats on those if they drum. The corrugated ribs already stiffen the floor and help stop vibration. Go straight to insulation: ST-Mat (see the next question).

Without battens, use only 3mm ST-Mat: it’s a soft rubber foam, and thicker layers compress over time so the plywood flexes. For thicker insulation, fit wooden battens and put thicker ST-Mat between them, or fill between the floor ribs with ST-Mat strips cut to the height of the ribs and cover the whole floor with 3mm. See the floor project.

No. Acoustic felt and acoustic foam are for dry areas only. Where moisture is possible, use closed-cell materials: ST-Mat is water-resistant and moisture-proof, and PPE ECO foam is water- and oil-resistant.

Yes. ST-Mat is fire-retardant, water-resistant and moisture-proof. Fire-retardant isn’t fireproof, though: keep all foam away from exhausts, turbos and other hot parts. We’ve used 10mm ST-Mat on the underside of a vintage car’s bonnet. See the bonnet advice.

Not if it’s done right. Closed-cell foam like ST-Mat and PPE ECO doesn’t absorb water, so bonded fully to the metal with no air gaps, it keeps moist air off the cold panels. Don’t put a plastic vapour barrier behind it, and ventilate the van (a roof vent or fan). Avoid fibreglass or loft wool against the metal: it soaks up moisture.

It depends on the vehicle and how much you treat. As a rough guide, brand tests typically show about 3 to 6 dB less noise from treating the doors alone, and more for a full vehicle. Most of the improvement comes from stopping panels drumming (Layer 1) and absorbing what’s left (Layer 3).

Measure each area you want to cover and work out the m². One big mat sheet covers 0.35 m² (about 2.9 per m²), an ST-Mat unit covers 1 m², and a felt sheet 0.40 m². The full list is in How much do I need? Or send us your measurements and we’ll help you work it out: WhatsApp +353 83 088 8713 or info@inshop.ie.