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Which Construction Foam to Choose

Construction foams are invaluable sealing and bonding materials. Their advantage lies in their readiness for use, easy installation, ability to fill gaps due to expansion, adhesion to various materials, good insulation properties, airtightness, improved soundproofing, etc. When browsing in stores and selecting construction foam, the options can be overwhelming. How do you choose the right one? As always with selecting construction materials, it’s essential to start with the type of work you intend to do and the role the construction foam should play in that work.

The easiest way is to go to the solutions page of justbuildit.eu and select the work that is planned to be done. It is possible to find the necessary products on the solution drawings, including construction foams.

Let’s go through typical construction solutions where construction foam is usually used and examine the essential properties needed in these applications, as well as what to consider when selecting and using foam.

Where Construction Foam is Used:

Installing windows

– Installing doors

– Filling various joints and gaps

Bonding plasterboard and other construction boards

Bonding facade insulation boards

Sealing and bonding window sills

– Bonding non-load-bearing internal walls with building blocks

– Bonding sauna insulation boards

– Sealing concrete formwork

– Fireproofing joints and penetrations

– Sealing penetrations

Sealing joints between insulation boards

Different Types of Construction Foams, according to Their Key Features and applications:

Gun Foams: Offer installation convenience, precise dosing, and speed. Gun foams generally have better yield than straw foams. Gun foam should be the first choice for responsible tasks. The quality of the foam gun also plays a significant role. A proper and clean foam gun ensures better structure and output.

Straw Foams: If you don’t have a foam gun at home and don’t intend to buy one, straw foam is the solution. It can be used without a gun, using a straw attached to the expanding foam canister. Straw foams are typically filling foams. A good choice for filling larger gaps and joints. Straw foam should be avoided if you plan to install openings or perform other tasks where higher expansion pressure and post-expansion might be problematic.

Multi-purpose: In addition to gun and straw foams, there are also combined solutions where a gun foam valve and adapter are suitable for both the gun and a special straw. For example, PENOSIL‘s EasyGun. The advantage of this straw is that it fits into narrower joints, such as between insulation boards. Generally, gun foam has the highest yield, straw foam has lower yield, and EasyGun falls between them in terms of yield.

Adhesive Foams: Specifically developed for bonding purposes. Although all foams are generally good adhesives, some may have unsuitable properties for bonding. For instance, lower tensile and compressive strength, excessive post-expansion, etc.

Fire-Resistant Foams: Should be distinguished based on fire sensitivity and fire resistance. Often these properties are present together, but not always. Improved fire sensitivity foams have reduced ignition sensitivity and fire spread. Fire-resistant fire foams are designed for filling joints and penetrations in fire barrier structures to prevent fire spread through the barrier. The properties and methods of using fire-resistant foams are indicated in the product documents.

High-Yield Foams: Developed to yield more meters or cubic meters of foam per can. The foam structure and density are adjusted to produce the maximum volume of finished product per liter or kilogram of chemicals. High-yield foams are essential for those concerned with the cost of finished work. One product can accomplish more work, and one work unit is usually cheaper. However, lower density is not always a virtue. Achieving some foam properties requires more polymer, resulting in higher density.

Elastic Foams: Necessary when there may be cyclic deformations on the foam installation joint or application area. For example, deformations due to temperature and moisture expansion of windows. See window installation section.

Spray Insulation Foams: Intended for smaller insulation tasks where traditional insulation materials cannot reach. Covering pipes and their surroundings, etc. Helps reduce heat loss and condensation risks. Before applying spray foam, surfaces must also be moistened. If multiple layers are planned, then the surface of the previous foam layer should also be moistened before applying the next layer. The thickness of one foam layer should not exceed two centimeters.

Guidelines and Tips. What to Know When Using and Choosing Foam:

– Foam must be protected from UV radiation.

– Cleaning the foam gun.

Special cleaners have been developed for cleaning the foam gun. Typically, they come in packaging similar to foam can, with an adapter for attaching to the foam gun. The kit also includes a spray nozzle. After finishing foam usage, clean the gun nozzle first, unscrew the foam bottle from the gun, attach it to the cleaner, spray the cleaning agent through the gun into a waste container until the cleaner starts coming out of the gun. Once these steps are done, let any excess cleaning agent and pressure out of the gun after some time, then tighten the gun. If not all foam was used and there are plans to use it again soon, the foam bottle can remain attached to the gun, and the regulator can be closed. However, the gun should not be left attached to the bottle for an extended period, as it can damage the gun when the foam inside curing.

– Removing cured foam.

Since mounting foams have excellent adhesion and cure quickly, cleaning contaminated surfaces is challenging. It’s easier to remove uncured foam with the designated cleaner, but for cured foam, it’s much more complicated. There are cleaners available for cured foam, but depending on the surface, it may not be successful or may damage and smear surfaces. Foam can also be mechanically removed from certain surfaces if the risk of damage is not significant. It’s generally advisable to cover adjacent surfaces at a safe distance before foam usage.

– Proper installation temperature is crucial for foam curing and quality.

The foam usage temperature is indicated on the product packaging. There are foams available for both subzero and high temperatures. Foams are usually classified as summer and winter foams accordingly. Choose the appropriate product according to the situation. Installation temperatures are indicated on the product packaging and technical documents. Moistening and cleaning surfaces are crucial. Polyurethane foam cures in the presence of moisture, and moisture helps ensure uniform foam structure. Surfaces where foam is applied or between which foam is sprayed must be clean from dust, ice, etc. Foam does not adhere to dusty surfaces.

– Shaking.

To ensure that the foam’s properties stated in the documentation are achieved, shake the foam bottle before use.

– PU Foam can temperature during usage, see the packaging.

Typically, the balloon temperature should be maintained at +15 °C to +20 °C for at least 6 hours before use. The balloon must not be heated by other means. For example, putting the foam canister in hot water can cause it to explode.

Mechanical properties. Depending on the application and the main purpose, a product with the necessary basic properties must be selected:

Density – Lower density generally provides better yield for foam. Higher density, however, provides greater pressure and tensile strength, and more material.

Compression and tensile strength are particularly important for adhesive foams.

Elasticity is generally important for larger deformations, such as window installation or movement joints.

Post-expansion indicates how much the foam expands after installation. A large post-expansion helps the foam fill necessary gaps but can be an unexpected surprise and smear surfaces.

Expansion pressure indicates the force generated by the foam’s curing on adjacent surfaces. For example, lower expansion pressure products should be used for windows and doors.

Water vapor permeability, adhesion, thermal conductivity, sound insulation, yield, etc., are also important properties. These should definitely be compared for different products before making a choice.

Typical application of using foam is window and door installation:

When installing windows, it’s important that the construction foam acts as thermal insulation and protects the joint from air leaks. For construction foam to work as good insulation, it must have a uniform structure. Figuratively speaking, there should be many tiny foam bubbles with as thin walls as possible between them.

Different foams have different structures. It’s often difficult to identify this at the store counter, and all packages usually claim to have good structure. The thermal conductivity declared in the product documents and on the package is usually a good indicator. The foam density stated in the product documents also somewhat indicates this property, but not always. Therefore, it is advisable, based on feeling and promises on the shelf, to choose one product, try it out, and then buy a larger quantity. For beginners, of course, it’s safest and cheapest to consult an expert.

The final shape of the foam, and therefore its properties, only emerge after installation and curing. It’s liquid in the bottle after all. Therefore, the surrounding environment, installation skill, and quality of the foam gun significantly affect the foam’s properties. Choose a construction foam suitable for the temperature. Since construction foam cures due to moisture, there may not be enough moisture in the cold, and the foam may not cure. Incorrect temperature also creates a bad structure in the foam and gaps.

Curing pressure.

When installing windows and doors, it’s important that the construction foam has low curing pressure. If the curing pressure is too high, there is a risk that the window and door frames will deform. Problems arise with opening and closing the fills and leaks and stresses occur. If necessary, the frames must be temporarily supported.

Foam elasticity and joint dimensioning.

Since the window is installed in the insulation zone and adjoins the facade structure, there are quite large deformations in this joint. Depending on the window material, it can expand and contract with temperature and humidity. The facade structure does the same. These movements usually sum up in terms of the foam joint, either compressing together or pulling apart simultaneously.

The foam used for window installation must have sufficient elasticity to withstand these deformation cycles over a long period without losing adhesion and tearing. It’s important to monitor and dimension the installation gap correctly. For example, too narrow a gap is dangerous from this aspect. If, for example, the deformation is 2 mm, there is a huge difference whether it occurs in a 1 cm or 2 cm foam joint. The deformation is then 20 or 10%, respectively. Accordingly, the appropriate construction foam must be selected.

Gun or straw foam.

For openings, gun foams should be used since their expansion pressure is generally lower. However, the expansion pressure of gun foams should also be compared because even gun foams have products with higher expansion pressure. Products with high expansion pressure should not be used for openings.

Foam cutting.

There is often a question of whether foam should be cut in the window joint or if the skin on the foam plays an important role in ensuring airtightness. The best result is indeed provided by precisely installed foam so that the joint is full (within the width of the frame) and does not need cutting. However, even cut foam is sufficiently dense in normal situations. The biggest mistake is made when attempting to push or smooth half-cured foam back into the joint. If the foam has not yet cured, any intervention damages the foam structure. This is much more harmful to foam airtightness than cutting it.

Generally, in today’s energy efficiency expectations, the foam joint should be additionally protected in terms of airtightness. Special tapes or coatings are used for this purpose. A product that is vapor-tight on the inside and wind-tight on the outside. Look at the window installation solution here: https://justbuildit.eu/ehituslahendused/


When installing openings, it is necessary to additionally moisturize the window frame and wall structure between which the foam is applied. Polyurethane foam cures under the influence of moisture, and moisture helps to ensure a uniform foam structure. Usually, there’s no need to worry about foam adhesion after moisturizing, but you don’t need a layer of actual water; spraying with a mist is enough.

If it’s a wide frame with a deep joint, then it’s worth applying the foam layer by layer, waiting a bit between each layer, and moisturizing. In the case of deep joints, moisture does not reach the foam evenly, and structural problems or higher expansion pressure occur.

Construction foam is not a window and door fixing material. Mounting foam is intended only for sealing openings. Fastening must be provided according to the designer’s and window manufacturer’s instructions, with mechanical fasteners. Adequate support and alignment blocks must also be used under and on the sides of the window according to the requirements.

Window installation accessories, airtightness tapes, sealants, etc.

As mentioned above, when installing windows, it’s advisable to use vapor and windproof tapes in addition to foam. Then the foam is additionally protected from moisture and wind. There is a lower risk of condensation and mold formation, resulting in a warmer joint and a healthier indoor climate. See the necessary products here:

Bonding construction boards to window jamb.

In addition to cement-based adhesives, adhesive foam can be used for bonding construction boards to window jamb. For adhesive foam, it’s important that it has low post-expansion, but despite this, the board must be temporarily supported and fixed.

Gluing window sills.

When gluing window sills with adhesive foam, the window sill must be additionally supported with plastic, plywood, or wooden support blocks. The compressive strength of the foam may not be sufficient.


When it comes to safety, it’s essential to read the manufacturer’s technical documents for foam products. It’s a container under pressure and usually contains flammable gases, making it potentially explosive. Many accidents have occurred, for example, from storing foam bottles loosely in cars or between sharp objects. There is a lot of trouble if it breaks or even if a small hole appears. To prevent the valve from sticking during the shelf life, the foam bottle should be stored upright. Foam products should only be used in well-ventilated areas – fire hazard and health risks.

For more detailed information, refer to the specific technical documents of the foam. Each product may have different guidelines and requirements to be followed.

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