Expanding Foam for Gaps, Frames, Insulation & Building Voids

The gap might only be 20 mm wide, but what happens inside it matters. Air leakage, heat transfer, noise, movement & an unfinished penetration can all turn a small opening into a bigger building problem.

Soudal PU foam provides Australian builders, installers, maintenance crews & trades with expanding foam options for filling cavities, insulating gaps, mounting window & door frames & sealing suitable service penetrations. Choose from convenient Genius applicators, professional gun-grade foam, straw-applied products, flexible formulations & an isocyanate-free alternative according to the job.

Working on openings that form part of the external building envelope? Explore Weatherproofing Supplies.

Need to trim cured foam or prepare surrounding materials? Browse Cutting Tools.

What Is Soudal PU Foam?

Soudal PU foam is a polyurethane expanding foam used to fill, seal & insulate suitable gaps, joints, cavities & openings in construction.

Applied from an aerosol can, the foam expands into available space then cures to form a stable fill. Depending on the product, it can help improve thermal insulation, acoustic insulation & airtightness around compatible building materials.

Soudal Australia's expanding foam range includes different application systems & performance types rather than one foam for every opening.

Options include:

► Soudal Pro Expanding Foam Genius – general-purpose gap filling with an integrated one-handed applicator
► Genius Gun Gap Filling Expanding Foam – controlled filling & insulation without a separate foam gun
► Gap Filling Expanding Foam – Straw – straightforward application for suitable general filling work
► Gap Filling Expanding Foam – Gun Grade – professional threaded format for controlled application through a foam gun
► Soudal Flexifoam Genius – flexible blue PU foam for joints where movement needs to be accommodated
► Flexible Insulation Foam – Gun Grade – flexible gun-applied PU foam for moving joints & higher-volume installation
► Soudafoam SMX – an isocyanate-free fixing foam for suitable cavity filling, insulation, frame installation & roof-construction applications

The differences matter. A static hole, moving window perimeter & deep non-porous cavity don't automatically call for the same product.

Why Choose Soudal PU Foam?

Expanding foam earns its place on site because it can reach irregular spaces that are awkward to close with rigid material alone.

Depending on the selected Soudal foam, benefits can include:

► Gap filling – expands into suitable holes, cavities & irregular voids
► Thermal insulation – helps limit heat transfer through unsealed openings
► Acoustic insulation – assists with reducing sound transmission through suitable gaps
► Airtightness – closes unwanted air paths within compatible building details
► Frame installation – selected products suit gaps around window & door frames
► Penetration filling – useful around appropriate pipes, cables & service openings
► Application choice – Genius, straw & gun-grade formats suit different workloads
► Controlled dosing – gun-grade products give experienced users precise bead control
► Movement capability – Flexifoam products remain elastic rather than becoming a conventional rigid fill
► Alternative chemistry – Soudafoam SMX provides an isocyanate-free option

The goal isn't to force the greatest possible quantity of foam into a cavity. Good application is about putting the appropriate amount of the right foam into the right opening.

Common Applications

Window & Door Installation

Frame perimeters can become pathways for draughts, heat transfer & noise if the surrounding gap is left untreated.

Soudal expanding foam can fill suitable spaces between window or door frames & surrounding construction while providing thermal & acoustic insulation.

But ask one question before selecting the can:

Will the joint move?

For a joint expected to flex as building materials move, Soudal Flexifoam Genius or Flexible Insulation Foam – Gun Grade provides elastic performance rather than relying on a conventional rigid cured foam.

Pipe & Service Penetrations

Pipes, conduits, cables & other services rarely create perfectly shaped openings.

Expanding foam can fill suitable irregular spaces around these penetrations while helping close air paths & improve insulation.

A penetration that requires fire resistance, waterproofing or another regulated performance characteristic needs the appropriate specified system. General-purpose PU foam shouldn't be assumed to provide those functions automatically.

Wall Cavities

Some spaces are easy to see but difficult to reach.

Expanding foam enters as a controlled bead then expands within the cavity, making it practical for suitable holes & voids where accurately cutting a rigid filler would be inefficient.

Avoid treating the cavity as a challenge to empty the can. Expansion needs to be allowed for during application.

Insulation Gaps

Insulation works best when the thermal layer isn't interrupted by uncontrolled openings.

Soudal expanding foam can close appropriate gaps around insulation materials, helping reduce draughts & unwanted thermal bridges.

Where movement is expected, flexible insulation foam can maintain the fill while accommodating movement within the joint.

Acoustic Openings

A surprisingly small opening can create an unwanted path for sound.

Soudal PU foams offer thermal & acoustic insulation properties, helping close suitable gaps around construction elements.

The foam remains one component of the complete wall, ceiling or floor assembly. It shouldn't be treated as a substitute for a properly designed acoustic system.

Roof Construction

Selected Soudal foams can fill suitable openings & connect insulation materials within roof construction.

Flexible Insulation Foam – Gun Grade is specified for filling cavities & sealing appropriate openings in roof construction while providing flexible performance.

Soudafoam SMX also lists sealing openings in roof constructions & connecting insulation materials among its applications.

For the weather-facing components of the roof system, browse Roofing Materials & Sealants.

Expansion & Moving Joints

This is where ordinary gap filling & flexible insulation separate.

A rigid cured foam can work well in a stable cavity. Movement changes the requirement.

Soudal's flexible foam technology is designed to compress & recover as suitable joints move, helping preserve insulation & airtightness.

Flexifoam Genius provides approximately three times the flexibility of standard PU foam while offering low expansion, minimal post-expansion & elastic performance.

Product Selection Guide

Forget the colour of the can for a moment.

Choose by answering these questions:

Is the gap static or moving?
How much application control do I need?
How much foam will I use?
Do I want an integrated applicator, straw or separate foam gun?
Does the project require a particular chemistry or tested performance?

Soudal Pro Expanding Foam Genius

For general filling without carrying a separate foam gun, Soudal Pro Expanding Foam Genius is a practical starting point.

Its built-in Genius applicator provides controlled one-handed application for jobs such as:

► Filling gaps & cavities
► Filling suitable joints
► Pipe penetrations
► Window & door frame installation
► Air sealing
► Thermal insulation
► Acoustic insulation

Once cured, the foam is water resistant & stable & can be cut, sanded, plastered or covered with an appropriate sealant.

A partially used can can remain usable for later work when stored & handled according to the product instructions.

Genius Gun Gap Filling Expanding Foam

This ready-to-use, one-component PU foam cures in contact with moisture & uses a trigger-controlled applicator.

It suits general tasks including:

► Gaps
► Holes
► Joints
► Frame perimeters
► Pipe penetrations
► Draught control
► Thermal & acoustic insulation

For application, the cavity isn't normally filled completely with wet foam. Allow for expansion rather than packing the opening from the outset.

Gap Filling Expanding Foam – Straw

Sometimes the simplest applicator is enough.

Straw-applied foam suits appropriate filling & insulation work where the installer doesn't need the control or repeated operation of a professional foam gun.

It's particularly useful for straightforward or occasional applications.

For repeated site work or situations requiring finer bead control, compare it with the gun-grade option.

Gap Filling Expanding Foam – Gun Grade

A separate foam gun changes how the material can be controlled.

Gun-grade foam suits professional users completing:

► Repeated applications
► Longer runs
► High-volume filling
► Frame installation
► Wall or roof void work
► Jobs requiring more precise dosing

The threaded canister connects to a compatible applicator so the operator can regulate the bead instead of relying on a basic straw.

Soudal Flexifoam Genius

Does the joint move?

That's the question Flexifoam is built around.

Soudal Flexifoam Genius is a flexible polyurethane expanding foam that cures elastically, allowing it to absorb movement in suitable substrates without behaving like a standard rigid cavity filler.

Key characteristics include:

► Approximately three times more flexibility than standard PU foam
► Elastic & compressible cured foam
► Low expansion
► Minimal post-expansion
► High filling capacity
► Thermal insulation
► Acoustic insulation
► Airtight performance
► Built-in Genius trigger
► Precise one-handed dosing
► No separate foam gun required
► Blue colour for easy identification

Typical applications include expansion joints, joints between wall panels, openings around window frames, wall cavities, holes & pipe penetrations where movement is expected.

Flexible Insulation Foam – Gun Grade

Need the same type of movement capability across larger or repetitive work?

Flexible Insulation Foam – Gun Grade combines elastic cured performance with a threaded canister for foam-gun application.

It's particularly relevant to:

► Moving joints
► Window & door frames
► Cavities
► Roof-construction openings
► Airtight sealing
► Thermal insulation
► Acoustic insulation

Like Flexifoam Genius, it provides around three times the flexibility of standard PU foam.

The main selection difference is application format: Genius for integrated one-handed dosing, gun grade for controlled higher-volume professional application.

Soudafoam SMX

Soudafoam SMX shouldn't be described as simply another flexible PU foam.

Its key distinction is different.

Soudafoam SMX is an isocyanate-free fixing foam with high thermal & acoustic insulation properties, strong filling capacity & excellent stability.

Suitable applications include:

► Filling cavities
► Sealing appropriate openings in roof construction
► Creating a sound-insulating barrier
► Improving thermal insulation
► Installing & sealing suitable window & door frames
► Connecting insulation materials

On porous materials such as timber, concrete & stone, the moisture-curing system performs best under the surface conditions specified by Soudal.

On non-porous surfaces, cavity depth becomes important. Soudal advises that deeper non-porous cavities beyond approximately 7.5 cm are better filled in separate stages with curing time between applications.

That is exactly why the product should be selected from the actual joint conditions rather than simply from the words “expanding foam”.

Expert Tips

Don't Fill the Entire Gap With Wet Foam

Expanding foam still has expanding to do.

For Soudal's Genius gap-filling foam, guidance calls for filling the cavity only partially before allowing the product to expand. Overfilling wastes material & creates unnecessary trimming.

A Moving Joint Needs a Moving Solution

Look at the building element rather than the empty space.

Window perimeters, expansion joints & other areas exposed to movement can benefit from flexible foam that compresses & recovers instead of relying on a rigid cured fill.

Match the Applicator to the Number of Gaps

One repair doesn't necessarily justify setting up a foam gun.

An integrated Genius applicator is convenient for intermittent work. A gun-grade can becomes increasingly useful where bead control, repeated starting & stopping or higher-volume application matter.

Moisture Plays a Role in Curing

Many expanding foams cure through interaction with moisture.

Follow the individual product's surface-preparation instructions rather than assuming every cavity should be treated exactly the same way.

Deep Cavities Need More Thought

A deep hole isn't automatically solved by injecting more material in one pass.

Product chemistry, substrate porosity & access to moisture can affect curing. Soudafoam SMX, for example, has specific guidance for deeper cavities on non-porous surfaces.

Don't Rush the Knife

Let the foam develop & cure sufficiently before trimming.

Cutting too early can disturb the foam structure instead of producing a clean finished edge.

Sunlight Changes the Finishing Requirement

Soudal Flexifoam isn't UV resistant.

Where cured foam will remain exposed to sunlight, finish or cover it with an appropriate compatible material rather than leaving the foam as the final exterior surface.

Check the Plastic Before Assuming Adhesion

“Plastic” covers very different materials.

Soudal's Flexifoam products provide adhesion across many building materials but list PE, PP & PTFE among the important exceptions. Identify the substrate first.

Fire-Rated Means Specified Fire-Rated Foam

Soudal's broader Australian range includes dedicated fire-resistant expanding foams.

If a wall, floor or service penetration needs a fire rating, don't substitute ordinary gap-filling foam simply because it physically fills the opening. Use the product & complete installation required by the tested fire-resistant system.

Check the Safety Requirements Before Application

Application convenience doesn't remove the need to handle expanding foam correctly.

Read the current product safety information, provide suitable ventilation & use the required protective equipment. For work where airborne exposure controls are required, browse  Respiratory Protection & Accessories.