Understanding The Dimensional Stability Of Spray Polyurethane Foam

Understanding The Dimensional Stability Of Spray Polyurethane Foam

The dimensional stability of insulation represents the ability of the product to maintain its shape and dimensions after exposure to extreme temperature and humidity conditions. Great variation in the volume of the insulating material (both shrinkage and expansion) can lead to several problematic situations on a construction site, including the inability to achieve the insulating performance required for the project with the product installed. In some cases, this can also lead to the complete restart of the works.

For spray-applied polyurethane foam, the CAN/ULC-S705.1-15 standard requires dimensional stability testing to assess product volume changes after exposure to each of the following conditions: 

• -20 °C; 
• 80 °C; 
• 70 °C with a relative humidity of 97% (±3%). 

For the product to pass the test, its results must be below the maximum volume change thresholds prescribed by the standard. 

SOPRA-SPF 200 and SOPRA-SPF 200 LT particularly stand out for their dimensional stability. The table shows that when tested at 70 °C with 97% (±3%) relative humidity, SOPRA-SPF 200 and SOPRA-SPF 200 LT are the products that offer the best stability compared to the other products available on the market. This means that the volume of the product does not vary greatly when exposed to these different temperatures. In other words, the product will remain stable. 

More specifically, in the last row of the table, the results mean that the volume of SOPRA-SPF 200 exposed to hot and humid conditions would only vary by 0.4%, while that of SOPRA-SPF 200 LT would vary by 2.8%. The volume variation increases significantly for the other products offered on the market, varying from 7% expansion to 13% in the highest case. According to the CAN/ULC-S705.1-15 standard, the maximum threshold to pass this test is 14%.

A change in volume, either shrinkage or expansion, could cause the insulation foam to delaminate from the substrate or generate sufficient tension to detach the air barrier membrane installed on the exterior support panel. When this phenomenon occurs, air can then infiltrate behind the insulating material, thereby reducing the overall thermal performance of the system and increasing the risk of air and moisture infiltration in the wall assembly. In other words, the assembly will be less efficient. In some cases, repair work will have to be carried out to remedy the situation, which could lead to additional costs and delays on the project. 

When sprayed insulation must be applied on membranes of the SOPRASEAL line, additional protection measures are recommended to prevent a possible delamination of the membrane caused by the curing of the insulating material. Metal bars can be mechanically attached to the perimeter of the building, to the transitions of the membrane, as well as around the frames of doors and windows and all other openings. 

Finally, although the performance of a spray polyurethane foam insulation is established in part by its LTTR (long‑term thermal resistance) value, other factors must also be considered, including dimensional stability, water absorption and air permeance, to name a few. It is important to consider a product as a whole to know its real overall performance as well as its contribution in the wall assembly. 

To learn more about the tests included in the CAN/ULC-S705.1 standard, you might like to read the following article: Understanding The CAN/ULC S705.1 And CAN/ULC S705.2 Standards Governing Medium-density Spray Polyurethane Foam