Thinsulate by 3M is a popular choice for insulating the interior of your van. The material is lightweight, resistant to mold and mildew, safe to touch and provides excellent acoustic insulation as well. The difference between SM400L and SM600L is the degree of loft. The 400L is about 1" thick and the 600L is about 1.5" thick.--
3M SM400L sound thermal insulation engineered for vehicles. 60" wide, scrim on one side. 1 linear foot is 5 square feet. Material comes compressed from 3M. The material will expand to 1" or 25mm. Thinsulate is FMVSS 302 certified (federal motor vehicle safety standard). Delivers more acoustic absorption per unit weight vs. competitive products. Helps customers meet mass reduction goals. Non-woven sound absorbing fibers create a quieter vehicle environment Hydrophobic fibers. Recommend using 3M 90 Adhesive Spray to apply the white fiber side to the van skin. Approximate amounts needed to insulate the walls, ceiling, doors and cab area of vans: Sprinter 144 WB = 50 linear feet, 170 WB Sprinter = 60 linear feet, 170 WB Extended Sprinter = 70 linear feet.