3M Foam Tapes

Closed-cell foam has sealed cell structure that resists air and moisture penetration, making it suitable for gasketing and sealing applications. Open-cell foam has interconnected cells that allow air passage, providing cushioning and sound absorption but not sealing capability. Select closed-cell foam when creating barriers against air, water, or dust; select open-cell foam when cushioning, acoustic, or ventilation properties are primary requirements.

Select tape thickness based on the gap being sealed plus allowance for compression. If surfaces are flat and gap is consistent, tape should be 30-50% thicker than the gap so it compresses adequately when fastened. For uneven gaps, tape must be thick enough to compress and seal at the largest gap while not being over-compressed at the smallest gap. Closed-cell foam provides more consistent compression characteristics than open-cell. Mock up the installation if uncertain about appropriate thickness.

Single-coated foam tape has adhesive on one side only; the foam itself contacts one surface while adhesive bonds to the other. Double-coated foam tape has adhesive on both sides, bonding the foam between two surfaces. Use single-coated for cushioning and gasketing where one surface needs protection or sealing without adhesive contact. Use double-coated for mounting and bonding applications where both surfaces should be adhesively attached. Most mounting applications use double-coated; most gasketing applications use single-coated.

For HVAC roof curb sealing, use closed-cell foam tape rated for outdoor use with UV resistance and temperature cycling capability. The foam must compress adequately to seal gaps while supporting the unit weight. EPDM and silicone foam tapes handle rooftop temperature extremes better than standard foam. Select tape thickness to accommodate gap size with appropriate compression (typically 25-50% compression for effective sealing). Open-cell foam is not appropriate since it absorbs water and loses sealing capability.