Everything You Need to Know About Polyurethane Mounting Foams
Complete guide about PU mounting foams for professionals.
What Are Mounting Foams?
Mounting foams, also known as polyurethane foams or PU foams, are one-component or two-component chemical sealants used in construction for insulation, filling, sealing, and installation tasks. They expand and cure upon contact with air moisture, forming a durable, insulating structure.
They are highly versatile and have become essential in modern construction work. Their unique properties make them suitable for a wide variety of applications, including:
Common applications include:
- Installing windows and doors
- Filling gaps and cracks
- Sealing pipe penetrations
- Insulating walls, ceilings, and roofs
- Soundproofing and thermal insulation
Types of PU Foams: Low vs. High Expansion, Gun vs. Straw
Polyurethane foams come in different expansion rates and application tools to match specific tasks. Understanding these variations helps ensure optimal results and minimize material waste.
| Foam Type | Expansion Rate | Application Tool | Best For | Why |
| Low Expansion | ~30-50% | Gun | Window and door installation | Low-expansion foam prevent frames deformation |
| High Expansion | 100%+ | Straw or Gun | Filling larger voids and general insulation | High expansion foam fill gaps |
Two component foams can be applied with two methods – gun or attached straw. What is the difference?
Gun PU Foams:
- Require a professional application gun
- Offer better control, precision, and yield
- Suitable for repeated use
Straw PU Foams:
- Come with an attached straw applicator
- Ideal for single-use or occasional applications
- Less precise
Best Foams for the Specific Job
Different construction tasks require different foam properties. Here’s a quick overview of which type to use based on the specific installation.
Best PU Foam for Door Installation
Proper door installation requires stability, precision, and protection from frame deformation. This is especially important for lightweight interior doors, where too excessive post-expansion could lead to misalignment or structural stress over time.
Use low-pressure, low post-expansion gun foams like Tytan Professional 65 or ULTRA FAST 70. These foams provide controlled expansion, fast curing, and excellent dimensional stability, making them ideal for installing interior doors without mechanical fixing.
Best PU Foam for Windows
Window frames are sensitive to distortion, so it’s essential to use gun foams with controlled post-expansion and reliable insulation values.
Choose foams with controlled post-expansion to avoid frame deformation.
Tytan ULTRA FAST 70 or Tytan Professional 65 are recommended for precision and insulation.
Best PU foam for Universal Fillings
For general construction gaps and cavities, select foams that offer high yield and versatility. These foams should adapt well to various joint sizes and surfaces.
Opt for high-yield, multi-season foams, such as Tytan Professional GUN or Tytan Professional STD.
Best Fire Stop PU Foam
In areas where fire resistance is required, the correct classification and certification are critical. Always verify product compliance with local fire safety regulations and use certified fire-retardant foams (e.g., B1 or B2 class).
PU Foam For Quick Thermoinsulation Patches
Sometimes you need to insulate hard-to-reach places, which can be challenging with materials such as mineral wool. Alternatively, you may need to insulate a small area. For quick fixes and small jobs, the best solution is single-component PU foam in a can.
Pro tip: products with a LOW‑MDI formula (Tytan Professional THERMOSPRAY) offer an easier and safer application process, as they don’t require special training and can be applied with basic protective equipment is sufficient.
Where PU Foams Won’t Work
While PU foams are extremely versatile, they also have limitations. Avoid using them in the following situations:
- Surfaces with active water leaks. In this case choose sealant which is dedicated to surfaces exposed to water.
- Direct exposure to UV without protection. If you leave the foam exposed to UV rays it will degredate.
- Areas requiring structural strength (like load-bearing gaps). Foams are dedicated to insulation not to the construction reinforcement.
Key Properties of PU Foam
Understanding the physical and chemical properties of polyurethane foam helps ensure it is used safely and effectively in different environments.
Is PU Foam Water-Resistant?
- Cured PU foam is water-resistant, but not waterproof.
- Cured foam must be protected with sealants or coatings for outdoor use, because constant exposure to water will lead to degradation.
Is PU Foam Flammable?
Most standard polyurethane foams are classified as B2, which means they have normal flammability according to DIN 4102-1 standards. They can ignite when exposed to an open flame or high temperatures.
For areas where fire safety is critical—like around electrical installations, partition walls, or escape routes—always use fire-rated foams (B1 class), designed to resist flames for a specified duration.
It’s important to remember that fire-rated PU foams are part of a fire-resistant system but do not make the whole assembly fireproof on their own. Always follow local building regulations and pair them with fire-resistant materials for complete protection.
How To Apply The Foam Correctly
No matter how advanced the foam formulation is, following the foam application good practices influence the result. To achieve parameters declared by the manufacturer always follow these essential tips common for most mounting foams.
General Tips:
- Shake can vigorously (30 times) to mix the internal ingredients properly
- Spray water on substrate
- Apply foam in layers for deep gaps
- Re-wet between layers
- Protect cured foam from UV and moisture
Foam Curing and Water Spraying
The curing time and proper hydration of PU foam during application are critical for performance and achieving manufacturers declared product parameters. Here’s what you need to know.
How Long Does Mounting Foam Cure?
The foam curing process largely depends on the formula design stage and the precise selection of chemical raw materials, which determine the reaction speed and structural stability. Gun-applied foams naturally cure faster, allowing further installation work to begin sooner.
Most manufacturers declare full curing after ~24h, however temperature and humidity may impact that time range. For example in cooler and dry conditions the foam will cure slower, than in hot and moist environment.
Luckily, for the professionals who are in the rush, there are fast curing mounting foams, which significantly speed up the process. For example, Tytan Professional ULTRA FAST 70 cures only 1.5 hour and is ready for cutting in ~20 minutes.
Why You Should Water Spray PU Foam Before And After Application
Water spraying might seem like an optional step – but for professional contractors, it’s absolutely essential when working with single-component polyurethane foam. Properly moistening the substrate before and after foam application (in temperatures above 0°C) plays a crucial role in how the foam cures, expands, and ultimately performs over time.
When you skip water spraying, you risk weak adhesion, poor insulation, and a brittle, uneven foam structure. Here’s why this step matters:
- Spray water before and after foam application when temperatures are above 0°C. One-component PU foams rely on ambient and substrate moisture to cure properly.
- Ensures the foam cures evenly and expands as intended, helping you achieve a dense and regular cell structure that maximizes insulation properties.
- Prevents shrinkage and cracking that may occur when there is insufficient moisture, especially in dry environments.
- Improves adhesion to building materials such as concrete, brick, wood, or ceramics, ensuring the foam bonds securely and doesn’t detach over time.
- Reduces the risk of air voids inside the foam, which can compromise both thermal and acoustic insulation.
This small step can significantly impact the durability and quality of your work—because as every pro knows, a proper seal starts with proper prep.
Most Common Mistakes When Applying PU Foams
Avoiding common mistakes with pu foam will help ensure the best performance from your foam application. Watch out for the following issues:
- Not wetting the foam before and after application. A mist of water ensure proper expansion, curing and foam structure.
- Applying too much foam at once can lead to waste, hinder the curing process and have a negative impact on the structure, potentially damaging the frames.
- Using the wrong foam for the season – when low temperatures arrive, choose products designed for cold conditions.
- Not protecting cured foam – UV exposure will lead to the foam degradation
- Improper can storage (incorrect temperature or position) can cause the foam to lose its properties, which will affect the final result.
How to Avoid Mold Around Windows
Mold around windows is almost never a coincidence — it’s usually the result of improper sealing and thermal bridging. When polyurethane foam is applied incorrectly, without proper surface preparation, water spraying, or protection from moisture and UV exposure, the joint can lose its insulation performance. This leads to air infiltration, condensation, and eventually mold growth around the frame. To prevent this, always choose the right foam for seasonal conditions, shake the can thoroughly, apply in layers, spray with water (for one-component foams), and protect the cured foam with appropriate interior and exterior sealing systems. Proper installation is not just about filling a gap — it’s about creating a durable, airtight and vapor-controlled joint.
How to Clean Areas Stained With Fresh and Cured Foam
If you have assembly foam stains on clothes, tools or other surfaces, it is important to act quickly. This will enable you to remove the stains almost completely. If the foam has already set, the situation is slightly more difficult and complete stain removal may be more challenging, but not impossible.
How can stains from fresh assembly foam be removed?
Spray the stained area with an acetone-based cleaner (e.g. Tytan Professional Polyurethane Foam Cleaner) and wipe the stain with a cloth. Then clean the area with water and a mild detergent.
How do you remove stains from hardened foam?
For hardened assembly foam, try removing the foam mechanically by gently scraping it off with a knife. Spray any remaining residue with a hardened foam cleaner (e.g. Tytan Professional Hardened Foam Cleaner), leave for about three minutes, then wipe off with a cloth, sponge or brush depending on the surface type.
Finally, clean the area with water and a little mild detergent.
How to care for a foam gun?
To ensure the long-term functionality and reliability of your foam gun, proper maintenance is key. Follow these simple but essential steps after each use:
- Always clean the gun using a dedicated PU foam cleaner immediately after use. This prevents cured foam from blocking the valve and nozzle.
- Store the gun with either a can of foam or cleaner attached. This keeps internal parts sealed and prevents air from entering, which can lead to blockages.
- Never leave the gun empty. An unsealed system can dry out quickly, reducing performance or damaging the gun permanently.
- Lubricate moving parts regularly if the gun is used frequently. This helps maintain smooth operation and prolongs the tool’s lifespan.
Protect Cured Foam
Once polyurethane foam has fully cured, it’s crucial to protect it to maintain its durability and insulating properties over time—especially in outdoor or exposed applications. Without proper protection, cured foam can degrade due to UV radiation, moisture, and temperature fluctuations.
- Always shield the foam with appropriate materials such as sealing tapes, liquid membranes, or protective coatings designed for construction use.
- UV and moisture protection is essential in all external applications, as prolonged exposure can cause the foam to crumble, discolor, or lose adhesion.
It is also worth remembering that covering freshly applied foam too quickly with additional layers, such as finishing compound or mounting tapes, can hinder the access of moisture from the air. Since moisture is essential for proper curing inside the gap, prematurely securing the surface can negatively affect the quality and speed of the entire process.
How to Storage and Transport PU Foam
Proper storage and transportation of polyurethane foam are essential to maintain product quality and ensure safe use on-site.
| Recommendation | |
| Position | Always store foam cans upright with the valve facing up |
| Temperature | Keep between +5°C and +30°C; avoid exceeding maximum limits |
| Transport | Protect from impacts, excessive heat, and direct sunlight |
Pro Tip: Never leave foam cans inside vehicles—especially during summer. Elevated temperatures can increase internal pressure, creating a risk of leakage or even explosion. Always store foam in a shaded, well-ventilated area to protect both the product and your safety.
Conclusion
Polyurethane foams are a must-have for any professional contractor. Choosing the right type, applying it correctly, and following proper storage and safety rules ensures durable, efficient, and professional results.
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