Up to 30% of a home's heat can escape through poorly insulated roofing. To address this, polyurethane foam, often called PU foam, provides an effective way to reduce heat loss, fill air leaks, and insulate without taking up too much space. It comes in various forms, including rigid panels, sprayed foam, and expanding foam in aerosol cans. Its cellular structure helps limit heat loss and improves the thermal comfort of a home. Polyurethane foam is commonly used to insulate walls, floors, underfloor spaces, attics, roofs, and other hard-to-reach areas. Sprayed foam adapts to irregular surfaces and seals air leaks, while panels are ideal for flat areas. Its major benefit is its strong insulating performance for a low thickness, which is especially useful when preserving living space is a priority. Expanding polyurethane foam is particularly useful for hard-to-reach areas where panels can't be installed. It is applied precisely in gaps and hardens to form a barrier against air infiltration. However, it does not replace complete insulation of walls or the roof. It can be used around cable passages, ducts, pipes, and window or door frames, as long as it doesn't block moving parts or ventilation devices. It helps fill cracks and reduce air currents that cause discomfort. Around pipes, it can reduce some noise from vibrations and air leaks, but it is not a true acoustic insulator. It should be applied sparingly, as its volume increases during drying, and excess can be trimmed after hardening. The right product depends on the intended use: sealing small gaps, bonding insulating elements, or filling larger cavities. It's important to check installation conditions, including temperature, exposure to moisture, and the type of surface. An unsuitable foam may not adhere properly, expand too much, or degrade over time. Monocomponent expanding foam, sold in aerosol cans, hardens when it comes into contact with air moisture. It is suitable for small joints and duct passages. The bicomponent version dries faster and offers more controlled expansion, which is useful in more complex situations. Foam adhesive is used to fix insulating panels or blocks without trying to fill large voids. Choose an aerosol with a nozzle for limited and accessible interventions. A spray application allows for more precise flow, less waste, and repeated use. Check the level of expansion indicated: low expansion helps prevent deformations around window and door frames. Ensure the product is compatible with wood, concrete, metal, or PVC, and resistant to moisture. Before applying expanding polyurethane foam, read the manufacturer's instructions and prepare a clean, dry, and dust-free surface. Wear gloves, goggles, and protective clothing, as the product can stick strongly to skin and surfaces. Ventilate the room well and work away from any flame or heat source, as the aerosol is flammable. If the instructions recommend it, lightly mist the surface to promote hardening. Fill joints and cavities to about one-third of their volume, as the foam will expand after application. Let it dry for the time specified, then cut the excess with an appropriate tool. Protect the hardened foam from UV rays with a coating, cladding, or appropriate finish. Polyurethane foam is effective for sealing and insulating, but it does not solve all insulation problems. It should not replace a dedicated insulation material for walls or the roof, nor should it block ventilation grilles, smoke ducts, drains, or fire barriers. For overall insulation or areas at risk of moisture, fire, or condensation, it's best to consult a professional to choose a suitable and durable solution.