Airtightness Tape: The Complete Guide to Airtight Tapes
What is Airtightness Tape?
Airtightness tape (also called airtight tape or air sealing tape) is a high-adhesion, fleece-backed tape used to seal the joints, junctions and penetrations that liquid membranes and sheet barriers can't reach on their own. It forms a permanent, flexible airtight seal across board joints, window and door reveals, service penetrations and steelwork — the weak points where most air leakage happens.
Our IM Fleece Airtight Tape is designed to work hand-in-hand with Passive Purple liquid vapour control membrane: the fleece backing bonds directly into the liquid membrane, creating one continuous airtight layer with no weak points.
When Do You Need Airtight Tape?
- Board and panel joints — sealing junctions between OSB, plasterboard and sheathing boards
- Window and door reveals — closing the gap between frames and structure, a major leakage path
- Service penetrations — pipes, cables and ducts passing through the airtight layer
- Steel and timber junctions — bridging dissimilar materials that expand and contract at different rates
- Membrane overlaps — joining sheet membranes or finishing the edges of liquid-applied areas
What Sizes Are Available?
IM Fleece Airtight Tape comes in 25-metre rolls in four widths: 75mm, 100mm, 150mm and 200mm. As a rule of thumb, choose 75–100mm for board joints and reveals, and 150–200mm for junctions, steels and movement-prone details.
How to Apply Airtightness Tape
- Make sure the surface is clean, dry and free of dust
- Apply the tape centrally over the joint or junction, pressing firmly from the middle outwards
- For the strongest result, coat over the fleece backing with Passive Purple or Passive Purple Brush so the tape becomes part of the continuous membrane
- On difficult substrates, prime first with Supergrip Primer
Airtight Tape vs Liquid Membrane: Which Do You Need?
It isn't either/or — they do different jobs. A liquid membrane like Passive Purple seals large surface areas seamlessly, while airtight tape handles the linear details: joints, edges and junctions. Most Passivhaus and airtight builds use both. A good rule of thumb: one roll of tape and one brush tin for every five tins of spray.
Frequently Asked Questions
Does airtight tape work on brick and blockwork?
Yes — on porous substrates use a primer first for maximum adhesion, or bed the tape into wet Passive Purple Brush.
Is it vapour-permeable?
The tape forms part of your vapour control layer on the warm side of the insulation, managing both air and vapour movement as part of the complete system.
How long does it last?
Applied correctly and coated into the membrane system, it is designed to last the lifetime of the airtight layer itself.
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Questions about your project? Speak to our technical team.