Features of polyurethane foam

Features of polyurethane foam

In the course of construction and repair, various materials and structures are widely used. But the same work invariably generates a lot of gaps and grooves, holes, especially if the repair is major. The solution in many cases is the use of insulating foam, the choice of which should be approached with the utmost care..


Polyurethane foam has become such a widespread attribute of modern construction and renovation that it is hard to imagine how they once worked without it.. Cylinders with an easily blown and instantly swellable reagent provide:

  • thermal insulation;
  • sound damping;
  • suppression of vibration;
  • sealing joints and joints;
  • overlapping cracks;
  • saturation of inaccessible cavities.

Polyurethane prepolymers are displaced from the cylinder with a special gas. The initially discarded substance is light and full of fine pores. But the inevitable contact with air accelerates the polymerization process and the transformation of polyurethane into the form of polyurethane foam. Simultaneously with the chemical transformation, the foam also changes physically, it takes up more and more space, hardens and hardens. Such a unique substance is extremely useful, but in order to achieve success, you should carefully study its technical characteristics..

The key parameters of any polyurethane foam are:

  • the discharged volume of the mixture (the figures on the cylinder refer to the ideal situation);
  • expansion level upon exit;
  • re-expansion (experienced by a substance in the process of polymerization);
  • number of pores;
  • adhesion to surfaces;
  • viscosity.

It has long been known that polymerized foam can take up many times more space than one that has just left the factory tank. Inexperienced or inattentive builders often cause serious damage for this reason. First of all, the risk concerns doors and windows, where a significant mass can press on a relatively thin structure. Professionals know that when the cavity is saturated, it is allowed to immediately direct there a maximum of 1/3 of its volume. If voids remain later, this can be corrected by adding additional foam, but only after hardening..

The density of the polyurethane foam is closely related to its expansion coefficient. The strongest and most stable seams are obtained using the material with the least secondary swelling. But the flip side of this choice is ultimately the increased consumption of the mixture. If the surface of the surrounding structures is quite hard, actively blowing foam can be used in order to save money. With regard to the formation of pores, this indicator directly affects the stability of the foam connection with other surfaces..

A high quality reagent should have 88% or more clogged pores. Another valuable property is excellent adhesion to almost all commonly used materials. But It is important to remember that even the best polyurethane foam does not stick to:

  • silicone;
  • polypropylene;
  • polyethylene;
  • teflon.

Viscosity for practical purposes is also quite important, it is even judged by it whether it will be possible to perform the work efficiently or not. Good viscous foams do not creep down under their own weight and adhere perfectly to the treated surface. But there is a nuance: if the temperature is higher or lower than the critical temperature for a given mixture, the viscosity can change significantly. This can be compensated by wetting the surface to be treated before starting work in order to increase adhesion. Better yet, work at the temperatures indicated on the packaging..

Drying time in most cases is 8 to 15 minutes. But it is still recommended not to touch the foam for at least 24 hours. When the surface hardens, you can already cut off part of the layer, cover it with plaster or paint. Normal shrinkage does not exceed 5%; if it is greater, the polymerizing material may be deformed and torn. Then there is no need to talk about high-quality sealing.. Additionally, it is worth learning everything about:

  • shelf life and service life of the coating;
  • fire resistance level;
  • compressive stress;
  • coefficient of thermal conductivity;
  • shear strength.


Polyurethane foam varies greatly depending on the type of specific composition. Taking the first cylinder seen on the shelf, you can be very disappointed in the result.. Polyurethane foam sealants are divided into two main types: two-component and one-component.. Single component reagents are the most common reagents. The polymer, when sprayed from a cylinder, hardens in about a day..

The exact curing time is determined by the amount of foam thrown out and the atmosphere. If you inject too much sealant into the cavity, the distant parts of the sealant cannot react with the air and remain liquid. The problem of one-component formulations, which cannot be eliminated with the current level of technology, is the short storage time. Uncontrolled chemical reactions can start inside the cylinder at any time. Structural or two-component foam is most often used by professionals, its essence is that the balloon is divided into two compartments, the border between which disappears only at the moment of activation.

The advantage of such a reagent is that it can be stored for quite a long time and finally hardens in 20-30 minutes. However, it is impossible to use the mixture in two or more doses. Therefore, two-component foam, in contrast to household foam, is chosen by installers of windows and doors, as well as by roofers. And then they only need it in cases where a lot of work is done. In general, choosing a professional option or not depends on many factors..

So, the packaging of highly specialized foams is made in containers from 0.75 liters, while household cylinders start from 0.3 liters. Therefore, you can focus on the amount of work. In a mass product, a part may remain inside the tank, and in the case of a professional product, this share is very small. In addition, it almost does not increase in volume, which makes it possible to more accurately estimate the need for foam. Half the shrinkage (up to 3% versus 5-7%) also makes the sealant quieter and more predictable for builders.

But the production of work with professional foam is impossible without a special gun, which is many times more expensive than a standard cylinder. This is fully justified by the increased accuracy of the work performed, which is especially important when forming thermal protection and when sealing joints.. Foam is also classified according to the mode of use.. So, a summer product works well at temperatures from +5 to +35 degrees; winter – from -35 to -10 degrees. Foam that can operate in the temperature range from -10 to + 35 is considered a universal option..

It should be borne in mind that these are just acceptable boundaries. When the sealant comes out of the cylinder at a low temperature, the amount produced is less than under normal conditions. But after hardening, the foam for any season will endure frost of 40 degrees and heating up to +90. Sometimes on the packaging there are proud inscriptions about “record yield” and the like. In fact, this is nothing more than a publicity stunt, because 1 kg of high-grade polymer can account for no more than 65 liters. And since the capacity of the cylinders reaches only 0.95 liters, minus the body, minus the displacing gas – the total amount of the product is limited to only 45 liters..

Professionals recommend carefully evaluating the shelf life and appearance of the purchased foam.. Any type of sealant excessively hardens and deteriorates during long-term storage. You can evaluate the quality by shaking the container and holding it in your hand. There should be something rolling inside without feeling excessive lightness. As for brands, here you can safely choose between the most advanced and well-known options..

Heat-resistant and fire-resistant polyurethane foam deservedly stands out in a special category. This material is intended to protect against fire as part of fire insulation. One-component mixture is initially ready for use, polymerized under the influence of atmospheric moisture. In addition to polyurethane foam, special reagents are added to it that block the spread of smoke and other gases that occur during combustion. A special kind of sealant does not drain from verticals and effectively copes with the saturation of any cavities.

To ensure the highest protection, developers are constantly thinking about improving adhesion to metal and glass, brick and cement, wood and polymer surfaces. Much in this regard has already been resolved. Compared to plain foam, heat-resistant foam is mechanically stronger, it tolerates moisture well (without the formation of mold nests). It lights up more slowly, and under the influence of open fire and heat only swells for a long time, but protects the substrate due to its low thermal conductivity.

It should be borne in mind that even resistance to flame and strong heating does not give resistance to ultraviolet radiation..

Big problems are often caused not only by fire, but also by liquid. It helps to fight her penetration into certain places. waterproof type of foam. The necessary properties are given to it by surfactants that form a mass of bubbles. Since less than 10% of all bubbles are open, it is very difficult for liquids to penetrate into the protective layer. But the problem is that the increased protection translates into a significant re-expansion. In addition, hydrophobic foams shrink faster than normal foams if temperature jumps occur..

Important: when the joints and parts touching water are sealed, the polyurethane that comes out cannot be cut off. Such a procedure will improve the appearance, but destroy the integrity of the layer and nullify the protective properties of the coating..

Waterproof foams are perfectly safe in living spaces, even in children’s rooms and kitchens. It is recommended to clarify in advance what the properties of a particular product are. Fire resistance and protection against electric shock do not always correspond to the required standards..

Waterproofing of wet surfaces with foam implies additional covering on top using enamels. On a waterproof product, unlike all other foam mixtures, saving is strongly discouraged. The safety rules when working with it are the same as usual. The technical communications are preliminarily brought to perfection, and only then the final finishing is carried out. Compliance with these simple requirements is extremely effective and improves the quality of work..

Deserves special mention all-season type of foam. Such a product came into use relatively recently, and not even all the leading concerns managed to master its production. The combination of the properties of a winter and summer product allows the sealant to be used quite calmly in almost any conditions. But it will still be better if you perform work in the temperature range from +5 to + 30 degrees, this improves the quality of polymerization. Universal foam will be suitable if the gap is between 1 and 8 cm.

Wetting the surface is recommended for those cases when work is carried out in winter. The reduced air humidity, which increases the setting time, is at least slightly compensated in this way. Water will definitely not become ice if you work quickly and carefully. For any type of sealant, the most attractive air humidity ranges from 60 to 80%.

A universal type of foam, due to its insignificant initial expansion, perfectly helps to put in fragile and thin structures, to close gaps in easily breaking materials.


Choosing a specific type of sealant is not too difficult, but knowing its properties is not enough to buy. It is also necessary to figure out how much of the mixture will need to be used in a particular case. The approximate figures are weighted averages for the most optimal process conditions. The slightest deviations in them or in the composition of the sealant lead to a completely different result.. It is useful to take into account that any flow rates per 1 m3 are given in descriptions and in technical documentation only for correct use:

  • along the seam, moistened with a spray;
  • when sealing adjacent parts with foam;
  • when shaking the bottle before use;
  • with the obligatory application of the sealant from the bottom point consistently upwards with a laying thickness of 3.5-4 cm in a uniform layer;
  • when the manufacturer’s specifications for temperature and humidity are strictly followed.

When a repairer moves a pipe or a pistol along a certain surface, the exact flow rate per meter does not only depend on the actual weather. The quality of the foam itself, the use and quality of the dispenser, the professionalism of the workers and the condition of the surface mean a lot. Even the geometry of the gaps or cavities to be closed is of no small importance. If the can is not shaken before spraying, not a light foam will come out of it, but a viscous heavy liquid. The total cost of the material will instantly increase, and at the same time, there is nothing to think about to achieve high-quality seams..

Scope of application

In addition to the flow rate, it is useful to know about the nuances of using polyurethane foam in a particular construction (repair) operation. A polyurethane based sealant can be used to close any void, crack or seam larger than 20mm. In addition to sealing gaps in windows, doors, walls and ceilings, this sealant mixture can help in other cases as well. Any use of foam indoors requires careful ventilation during all processing, and ideally until the sealant has completely solidified.. Foam treatment is used when it is necessary to lay and insulate:

  • pipelines;
  • electric wires;
  • other communications.

The porous composition makes the mixture attractive for thermal protection of cooling, heating, plumbing and air conditioning systems. It is easy to use foam to cover the crevice in the roofing material, to insulate a cold room, to fix certain types of panels and sheets attached to the walls. Where surface adhesion is low or very precise dosage is required, it is advisable to use a professional grade sealant..

The fewer pores in the released mass, the better the containment of cold or heat. In addition, the reduction in pore size helps to make the foam stronger and more resistant to temperature jumps and active sun exposure..

Drying time

It is extremely difficult to predict exactly how quickly the foam will dry. But there are a number of common points that cannot be ignored.. The key significant factor is the humidity of the environment and the surface.. Unlike paint, varnish or enamel, foam dries faster the higher the humidity level. After all, a polymerization process takes place in it, in which water is one of the most important components. Drying times are predictably shorter at high temperatures.

As a result of a series of experiments and observations of practical construction situations, it was found that the polymer precursor hardens (at a thickness of 50 mm) for a maximum of 3 hours. But even after that, the process of hardening of the polymer itself continues, it will take at least 2-3 times more time. Under unfavorable conditions (frost and dryness), the total drying time increases to a day. Therefore, experienced builders never rush to finish finishing surfaces that have been sealed with foam..

Periodic hydration helps speed up the process a little, but nothing more..


In order not to endlessly face problems after hardening and throughout the entire period of operation, it is very important to choose the right brand. The rating in Russia is naturally topped by the brand “Moment”. The line of this manufacturer includes a number of interesting options. For example, “Montage” does not require a special pistol to use, and, according to the manufacturer, all modifications tolerate ultraviolet rays quite well. There are all-season, professional, and professional all-season versions, and even a fire-resistant version..

Company Profil offers both pistol and amateur (pipe) solutions. The pistol version is supplied in a container with a capacity of 0.625 liters. Quite good market positions have Makroflex Standart. The product is easily found in stores even in the most remote corners of the Russian Federation. Foam adheres perfectly where needed and minimizes re-expansion.

Tips & Tricks

When using polyurethane foam, many subtleties are found that are not written about on the manufacturers’ websites and in the attached instructions. Or they write, but many unreasonably ignore these instructions. If the product is planned to be used in severe frost, it is better to heat the container by placing it in warm water. Optimal warming up is up to 5 degrees. If absolutely necessary, you can cut off the excess foam mass one hour after application.

It is possible to improve the quality of waterproofing if the surface is pre-treated with grout. The same compounds as for moisture protection can be used for sound insulation in any room. Rags help to remove excess portions of the substance, but it is better to avoid smearing the foam. The hardened excess is removed with any solvent. Foam on your hands is removed with an aqueous solution of sodium chloride, laundry soap or vegetable oil.

Hand contamination is easy to prevent, you just need to wear protective gloves. It is important to understand that the foam mass alone cannot solve all the sound problems in the room. A comprehensive study of protective measures will be required, but for blocking cracks and holes, it is the sealant that is the best choice. Often people are interested in whether expired foam can be used. The answer is no – there may be a poor yield, and a loss of valuable qualities, and excessive shrinkage, and incomplete polymerization..

For an overview of the recommendations for the use of polyurethane foam, see the following video.

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