Choosing the Right Membrane Sealing Tape: Single-Sided, Double-Sided or High-Performance Vapour-Open Tape?

Single-Sided, Double-Sided and High-Performance Exterior Sealing Tapes: Understanding the Difference

Membrane sealing tapes are often grouped together because they all appear to perform the same basic task: sealing overlaps and joints. In practice, however, a single-sided seam tape, a double-sided lap tape and a high-performance vapour-open exterior tape control the joint in different ways.

The correct tape should be selected according to joint geometry, substrate type, exposure conditions, required inspection method and the role of the sealed layer within the wall or roof assembly.

This guide compares three Vantell products:

• VSST Series Acrylic Single-Sided Sealing Tape
• VDST Series Acrylic Double-Sided Sealing Tape
• Vantell AeroSeal EX High-Perm Exterior Acrylic Tape

Although all three products can contribute to improved continuity at membrane joints, they are not direct substitutes for one another. VSST is a visible surface-applied seam tape, VDST is a concealed double-sided lap tape, and AeroSeal EX is a higher-specification exterior tape intended for more demanding vapour-open airtightness and weather-sealing details.

Why Membrane Joints Need More Than Simple Adhesion

A weather-resistive barrier, breathable membrane or air-control layer can only perform correctly when it remains continuous across the entire building envelope.

The main field of the membrane may provide suitable water resistance, vapour permeability or air-control performance, but the assembly can still be weakened by poorly sealed:

• Horizontal and vertical overlaps
• End laps and cut edges
• Membrane terminations
• Sheathing board joints
• Window and door perimeters
• Pipe, cable and duct penetrations
• Inside and outside corners
• Transitions between flexible membranes and rigid substrates
• Installation cuts, tears and local repairs

At these locations, the tape must do more than simply stick to the surface. It must maintain contact under temperature changes, construction movement, wind pressure and changes in substrate geometry.

The most important selection question is therefore not:

Which tape has the highest peel adhesion?

A more useful set of questions is:

• Is the joint membrane-to-membrane, membrane-to-board or board-to-board?
• Will the tape sit over the joint or inside the overlap?
• Must the completed seal remain visible and inspectable?
• Does the tape need to bridge an actual gap?
• Will it be exposed to UV and weather before cladding is installed?
• Is low-temperature installation expected?
• Must the exterior assembly remain vapour open?
• How much bonded width is available on each side of the joint?

Three Different Joint-Control Methods

1. Surface Sealing with a Single-Sided Tape

A single-sided tape is installed over the face of a joint. One part of the adhesive bonds to one side of the seam, while the remaining part bonds to the other side.

This creates a visible bridge over the discontinuity. The finished detail can be inspected for alignment, wrinkles, edge lifting and adequate bonded width.

This method is commonly used for:

• WRB and housewrap seams
• Breathable membrane overlaps
• Vapour-control-layer joints
• Local membrane repairs
• Visible air-sealing details

The main advantage of a single-sided tape is that it directly covers the joint from the surface. It is generally easy to inspect and straightforward to apply on flat, regular membrane seams.

2. Concealed Bonding with a Double-Sided Tape

A double-sided tape is installed between two overlapping membrane layers. The lower adhesive surface bonds to the first membrane, and the upper adhesive surface bonds to the second membrane after the release liner is removed.

The completed tape remains hidden inside the overlap. This creates a clean exterior appearance and helps hold the two layers together before battens, cladding supports or other permanent fixing components are installed.

This method is commonly used for:

• Membrane-to-membrane overlaps
• Concealed WRB lap joints
• Breathable membrane laps
• Temporary positioning during installation
• Reducing movement and flutter at overlaps

A concealed double-sided bond is not the same as a surface bridge. The tape depends on close contact between two overlapping surfaces and does not automatically cover the exposed edge of the upper membrane.

It is therefore less suitable for open board joints, irregular transitions, penetrations or details where the tape must span a gap between different materials.

3. Exterior Airtightness Detailing with a High-Performance Vapour-Open Tape

A high-performance exterior tape is normally surface applied, but its role is broader than ordinary membrane lap sealing.

It may be required to connect flexible membranes to rigid sheathing, bridge board joints, seal window and door transitions, form airtight connections around penetrations and remain bonded during prolonged construction exposure.

In a vapour-open wall assembly, the tape must also support continuity of the air- and weather-control layer without unnecessarily restricting outward drying.

This is the position of Vantell AeroSeal EX. It should not be understood as only a stronger version of a general-purpose seam tape. It is intended for a wider and more demanding exterior application range.

VSST Series: General-Purpose Visible Seam Sealing

VSST Series is a single-sided acrylic tape designed for standard membrane seams, overlaps and local repairs.

It is applied over the face of the joint, making the completed seal visible. This allows installers to confirm that the tape is centred over the seam and that sufficient bonded area has been maintained on both sides.

Typical VSST Applications

• Housewrap and WRB seams
• Breathable membrane overlaps
• Vapour-control membrane joints
• Small membrane cuts and repairs
• General membrane-to-membrane surface sealing

Where VSST Performs Best

VSST is most suitable for relatively flat and regular joints where both sides of the seam provide sufficient bonding area and where the tape does not need to accommodate the broader exposure, substrate and detailing requirements of a premium exterior system tape.

Its main advantages are:

• Simple surface installation
• Visible and inspectable sealing
• Suitable for standard membrane overlaps
• Useful for local repairs and cuts
• Efficient for routine WRB installation

Limits of a General-Purpose Seam Tape

A standard seam tape should not automatically be used for every exterior connection.

More demanding applications may involve:

• Rough or porous sheathing boards
• Open joints between panels
• Changes between flexible and rigid substrates
• Low-temperature installation
• Extended UV and weather exposure
• Window and door perimeter detailing
• Penetrations and three-dimensional geometry
• Greater movement or installation tolerance

In these conditions, tape backing strength, conformability, substrate wetting, tape width and weathering capability become more important.

VDST Series: Concealed Membrane Lap Bonding

VDST Series is a double-sided acrylic tape designed to be installed between overlapping membrane layers.

Its main function is to create a concealed bond within the lap rather than to bridge the joint from the outer surface.

What VDST Does

• Bonds the upper membrane layer to the lower layer
• Helps keep overlaps closed during installation
• Reduces membrane flutter and movement
• Helps limit air movement through the lap
• Helps reduce wind-washing behind the membrane
• Maintains a clean outer membrane appearance
• Assists temporary positioning before permanent fixing

Why Concealed Bonding Can Be Useful

Lightweight membranes may move under wind pressure before battens, fasteners or cladding supports are installed. A double-sided tape helps stabilize the overlap and keeps the upper and lower layers in close contact.

Because the tape remains protected inside the lap, it is not directly exposed on the outer face of the membrane.

This makes VDST particularly suitable where:

• The detail is a regular membrane-to-membrane overlap
• A concealed joint is preferred
• The membrane needs temporary positioning
• The overlap already follows the correct water-shedding direction

Why VDST Is Not a Universal Final Joint Tape

A concealed double-sided tape cannot be inspected as easily after the upper membrane has been pressed into place.

Contamination, wrinkles, insufficient pressure or incomplete contact inside the overlap may not remain visible once the joint is closed.

VDST is also not designed primarily to bridge:

• Open sheathing joints
• Gaps between different materials
• Irregular penetrations
• Recessed or uneven surfaces
• Membrane terminations with limited overlap

Its correct role is concealed lap bonding and overlap control, not replacement of every surface-applied exterior sealing detail.

AeroSeal EX: High-Specification Exterior Airtight and Vapour-Open Sealing

Vantell AeroSeal EX is positioned as a higher-specification exterior acrylic tape for demanding building-envelope connections.

Its application scope extends beyond ordinary membrane seams. It is intended for exterior airtightness and weather-sealing details involving membranes, sheathing boards and transitions between different materials.

Typical AeroSeal EX Applications

• Exterior sheathing board joints
• WRB and breathable membrane seams
• Membrane-to-board transitions
• Window and door perimeter connections
• Pipe, cable and service penetrations
• Inside and outside corners
• Repairs requiring wider coverage
• Exterior air-barrier continuity details
• Vapour-open wall and roof assemblies

Why AeroSeal EX Is a Higher-Level Product

The difference between AeroSeal EX and a standard seam tape should not be reduced to one peel-adhesion value.

A high-specification exterior tape must be assessed as a complete combination of:

• Backing strength
• Backing conformability
• Adhesive wetting and long-term bond development
• Substrate compatibility
• Low-temperature application capability
• UV and construction exposure resistance
• Available tape widths
• Vapour permeability
• Suitability for both flexible and rigid substrates

Broader Substrate Capability

A regular membrane overlap normally involves two similar flexible materials. A high-performance exterior connection may involve dissimilar materials with different textures, surface energies and movement characteristics.

Examples include:

• Non-woven WRB to wood-based sheathing
• Membrane to cement board
• Membrane to aluminium or coated metal
• Board-to-board sheathing joints
• Membrane to window or door frames

AeroSeal EX is intended for this wider application range, where the tape must connect materials rather than simply seal two similar membrane surfaces.

More Robust and Conformable Backing

The backing of an exterior tape is not only a carrier for the adhesive. It also transfers stress across the joint and allows the tape to bridge changes in substrate geometry.

At an open board joint, penetration or material transition, the backing becomes part of the functional detail.

A conformable non-woven backing can follow minor substrate irregularities and changes in plane more effectively than a rigid film, making it useful for:

• Corners
• Window transitions
• Board joints
• Penetrations
• Uneven surfaces

Wider Tape Options

Tape width directly affects the available bonding area on each side of a joint.

A 50 mm tape may be suitable for a straight and regular membrane seam. Wider 75 mm and 100 mm tapes can provide additional bonded area and greater installation tolerance for:

• Sheathing joints
• Window and door perimeters
• Membrane-to-board connections
• Penetrations
• Repairs
• Uneven or irregular transitions

Wider tape is not automatically better, but it becomes important when the detail cannot reliably provide sufficient bonding area on both sides.

Low-Temperature Application

Pressure-sensitive acrylic adhesives depend on effective wetting of the substrate. At low temperatures, the adhesive becomes less able to flow into the surface texture, which can reduce initial tack and delay bond development.

A tape developed for cold-weather installation must maintain useful initial adhesion and substrate wetting under more demanding site conditions.

AeroSeal EX is designed for installation at temperatures down to approximately -20°C, giving it a broader application range for winter construction and cold-climate projects.

Extended UV and Construction Exposure

Exterior tapes are often installed before the final cladding system is completed.

During this period, the tape may be exposed to:

• UV radiation
• Rain
• Wind pressure
• Daily temperature cycling
• Construction delays

AeroSeal EX is designed for temporary UV exposure of up to approximately 180 days, making it more appropriate for projects where extended construction exposure is an expected condition.

This does not mean the tape should remain permanently uncovered. It means the product provides a wider construction exposure window than a basic lap tape.

Vapour-Open Exterior Detailing

A vapour-open tape is designed to restrict uncontrolled air and water entry while still permitting water vapour diffusion through the sealed area.

This is important because airtightness and vapour resistance are not the same property.

• Air leakage is bulk movement of air through gaps, cracks and unsealed joints.
• Vapour diffusion is molecular movement of water vapour through a material.

A material can be highly airtight while still remaining relatively open to vapour diffusion.

In a vapour-open wall assembly, this allows the sealed exterior layer to limit convective moisture transport while preserving outward drying potential.

AeroSeal EX is therefore particularly suitable where the WRB or exterior sheathing layer forms part of a vapour-open air- and weather-control strategy.

The Difference Between Bonding and Bridging

One of the most important distinctions in tape selection is the difference between bonding an overlap and bridging a discontinuity.

Bonding an Overlap

When two membrane layers overlap, the surfaces are in direct contact.

A double-sided tape such as VDST bonds these layers together within the lap. The membrane itself continues across the joint, and the tape helps control the contact between the overlapping surfaces.

Bridging a Discontinuity

At a sheathing joint, penetration or membrane-to-board transition, there may be an actual gap, open edge or change of material beneath the tape.

The tape must span this discontinuity while remaining bonded on both sides.

In this situation, the backing strength, width and flexibility of the tape become essential.

AeroSeal EX is more suitable for this bridging function because it is designed as an exterior detailing tape, not only as an adhesive layer hidden inside a lap.

Why Peel Adhesion Alone Is Not Enough

Peel adhesion is a useful comparison value, but it does not describe the complete performance of a sealing tape.

A laboratory peel result does not by itself explain:

• Initial tack during cold-weather installation
• Long-term bond development
• Resistance to sustained loading
• Performance on dusty or porous boards
• Compatibility with membrane coatings
• UV ageing
• Water exposure at tape edges
• Backing movement and stress distribution
• Adhesive creep under heat
• Performance across irregular joints

A tape with high peel adhesion can still fail if it is installed on a contaminated surface, applied without sufficient pressure or used across a joint beyond the capacity of its backing.

Conversely, a correctly selected tape with moderate peel adhesion can perform well when the joint geometry, surface preparation and installation conditions are properly controlled.

Understanding Airtightness at Membrane Overlaps

A membrane overlap may shed liquid water effectively while still allowing air movement.

Wind pressure can drive air behind a loose or unsealed lap, potentially causing:

• Wind-washing of insulation
• Membrane flutter
• Convective moisture transport
• Pressure leakage through the exterior layer
• Reduced thermal performance near the membrane surface
• Additional stress around fasteners and edges

Both single-sided and double-sided tapes can help improve lap control, but they do so differently.

VSST covers the seam from the surface. VDST bonds the two layers inside the overlap. AeroSeal EX can cover the seam while also extending the same exterior air-sealing approach to boards, frames, penetrations and other transitions.

Inspection and Quality Control

The ability to inspect a completed joint is an important difference between tape types.

Single-Sided Tape Inspection

A surface-applied tape such as VSST or AeroSeal EX remains visible after installation.

The installer can check:

• Whether the tape is centred over the joint
• Whether sufficient bonding width exists on both sides
• Whether wrinkles or fish-mouths are present
• Whether the tape edges are fully bonded
• Whether the tape has been properly rolled

Double-Sided Tape Inspection

A double-sided tape such as VDST becomes concealed after the upper membrane is applied.

Quality control must therefore take place during installation. The installer should confirm:

• Correct tape alignment before closing the lap
• Removal of the release liner
• Clean and dry membrane surfaces
• Firm pressure across the overlap
• No wrinkles or folds inside the joint

Once the overlap has been closed, internal bonding defects may be difficult to identify.

Substrate Preparation and Adhesive Wetting

Pressure-sensitive acrylic adhesives require close contact with the substrate.

The surface should be:

• Clean
• Dry
• Stable
• Free from dust
• Free from oil and release agents
• Free from frost and condensation

Dusty or porous sheathing boards can be particularly difficult because loose surface particles may separate from the board after the tape has been applied.

In these cases, adhesion to the dust layer is not the same as adhesion to the structural substrate.

Project-specific adhesion testing should be considered for:

• Very porous boards
• Weathered sheathing
• Coated metal surfaces
• Low-surface-energy membranes
• Cold or damp substrates
• Unfamiliar construction materials

Pressure During Installation

Acrylic adhesive tapes are pressure sensitive. Firm rolling helps the adhesive flow into the microscopic texture of the substrate and increases the actual contact area.

Simply placing the tape on the surface is not enough.

The installer should:

1. Apply the tape without excessive tension.
2. Keep the tape centred over the joint.
3. Press the tape firmly from the centre toward the edges.
4. Use a roller or suitable application tool.
5. Check the tape edges for incomplete contact.
6. Avoid creating wrinkles or trapped channels.

Over-stretching the tape should also be avoided because stored tension can later pull the tape away from corners, edges or changes in plane.

Common Failure Modes

Insufficient Bonding Width

If too little tape is bonded to one side of the joint, movement or substrate irregularity can concentrate stress at the edge.

Contaminated Substrates

Dust, moisture, oil, frost or loose particles can prevent proper adhesive wetting.

Wrinkles and Fish-Mouths

Wrinkles can create channels that allow air or water to pass behind the tape.

Incorrect Tape Position

A double-sided lap tape may be incorrectly used where a surface bridge is required, or a narrow seam tape may be used where a wider transition tape is more appropriate.

Low-Temperature Application Beyond Product Capability

A tape may appear attached at low temperature but fail to develop a stable bond if the adhesive cannot adequately wet the substrate.

Excessive Construction Exposure

UV exposure and weathering beyond the permitted construction period can degrade the tape backing or adhesive system.

Movement at Unsupported Joints

A tape should not be expected to compensate for excessive panel movement, unstable substrates or poorly designed gaps.

Product Comparison

When to Choose VSST

Choose VSST when:

• The joint is a regular WRB or membrane seam.
• A visible surface-applied seal is preferred.
• The tape must be easy to inspect.
• The substrate is relatively flat and regular.
• A standard 50 mm tape provides sufficient bonded width.
• The application does not require extended UV exposure or complex board transitions.

When to Choose VDST

Choose VDST when:

• The tape must be concealed inside the overlap.
• The joint is membrane-to-membrane.
• A clean exterior membrane surface is preferred.
• The overlap needs temporary positioning before mechanical fastening.
• The tape is being used to reduce movement and improve contact inside the lap.

When to Choose AeroSeal EX

Choose Vantell AeroSeal EX when:

• The joint forms part of a defined exterior air-control layer.
• The detail involves sheathing boards or rigid substrates.
• The tape must bridge an open joint or material transition.
• Window, door or penetration detailing is required.
• The assembly must remain vapour open toward the exterior.
• Cold-weather installation is expected.
• Extended construction exposure may occur.
• Wider tape is needed for greater bonding area.
• A more robust and versatile exterior sealing system is required.

Can Two Tape Types Be Used in the Same Joint?

In some assemblies, a double-sided tape and a single-sided tape may be used together.

For example, VDST may be installed inside the membrane overlap to hold the layers together, while VSST or AeroSeal EX may be applied over the outer face where a visible final seal is required.

This should not be treated as a universal requirement. The decision depends on:

• The membrane system design
• The required air- and water-control function
• The overlap direction
• The substrate condition
• The exposure level
• The project specification

The key principle is that each tape should perform a defined function rather than being added without a clear detailing purpose.

Conclusion

VSST, VDST and AeroSeal EX represent three different approaches to controlling membrane and exterior building-envelope joints.

VSST is a visible, general-purpose single-sided tape for routine membrane seams and repairs.

VDST is a concealed double-sided tape for bonding overlapping membrane layers and supporting installation control.

Vantell AeroSeal EX is a higher-specification vapour-open exterior tape for demanding airtightness, sheathing, window, door and penetration details.

The correct choice should be based on the actual function of the joint rather than tape appearance alone.

For routine membrane seams, VSST provides a practical and inspectable solution. For concealed lap bonding, VDST offers a clean and effective joint configuration. For high-performance exterior envelope continuity across membranes, boards and complex transitions, AeroSeal EX provides the broader application and performance platform.

For project-specific recommendations, contact Vantell with information about the membrane type, substrate, joint configuration, climate, installation temperature and required exposure period.