What is Polyurethane Foam?

Polyurethane (or PU) foam is a polymer, made from two components, polyol and isocyanate, which are both oil derivatives. PU foam can be produced with different properties:  open or closed cell, and rigid or flexible.  Additives may be used to create or manipulate different properties, such as fire retardation, or accelerants to decrease final density, etc.

How safe is Polyurethane Foam?


Polyurethane is a very stable and well-documented material. As long as production regulations and safety measures such as the use of PPE (Personal Protective Equipment) directives are followed, the production of polyurethane foam is as safe as any other industrial spray process, such as automotive spray painting.


PU Foam is inert. This means that under normal conditions, it is chemically inactive.  Polyurethane is so stable that it is used as lining for freshwater applications.

Fire Risk

As with any oil-based polymer, it is possible to produce ignition in PU Foam.  For applications where there is an appreciable fire risk, such as insulation of dwellings, safe fire retardants are added to the PU.  For underground pipeline applications, where there is little fire risk, fire retardant may not be added.

More Information

The best source of up-to-date information regarding PU foam is available from ISOPA, which is the European trade association for producers of isocyanates and polyols.

How strong is Polyurethane Foam?

The Velocifoam applications use a rigid, closed-cell PU foam.

The compressive and tensile mechanical strengths of our PU foams are similar, and proportional to the density.  The final density can be manipulated by controlling production values, such as pressure & temperature, and by the use of additives, to control the amount of gas produced; this gas forms the bubbles in the foam.  The more gas, the larger bubbles, and the lower the density.

In our standard applications, we aim for a density of 0.045 SG, or 45kg/m3, or 2.8lb/ft3.  At this density, the compressive and tensile strengths of the foam are around 300kPa, or 43.5psi, using international standards EN826 and EN1607.

What does that mean in practical terms?

In layman’s terms, this means that a grown man could stand on a cupcake-sized cube of foam measuring 5 cm or 2 inch square without it collapsing.  Or, a 25 cm or 10 inch square section of foam could suspend a 2017 Jeep Wrangler.

How well does Polyurethane Foam stick?

Adhesion is a complex area of science, and a full explanation of every aspect is beyond the scope of this FAQ.  However, in the VelociFoam systems, there are two main forms of adhesion: mechanical and chemical.

Mechanical adhesion occurs when the first few molecular layers of polyurethane interlock with a surface, like a filling in a tooth, and chemical adhesion results from the forming of compounds between the surfaces of the PU and the substrate (the surface of the pipe or cable.)

Depending on the substrate and other factors affecting adhesion (see next ), we expect adhesion of 300-800 kPa or 45 – 115 psi under well-controlled conditions.  This allows for very strong local forces that might cause damaging movement in pressurised pipe systems to be taken up by the foam and transferred or dissipated into the entire buried system.  Critically, it allows unrestrained pipe jointing systems to act as restrained systems, by effectively gluing pipe sections to each other across couplers.

Factors affecting adhesion

Adhesion is also affected by local atmospheric conditions:  temperature and humidity.  Colder, wetter surfaces result in lower adhesion.  Consequently, our installation instructions contain strict values for correct installation, where adhesion is required for acceptable mechanical performance of the system.  For example, where GRP (glass reinforced polyester) pipes are installed in a pressurised system, and adhesion is important, the pipe surface must be clean and the pipe temperature should be brought up to a level that ensures sufficient bonding for the required system performance.  This can be achieved with the use of various measures, such as direct pipe heaters or overnight storage in controlled conditions.