What type of insulation is commonly used in SIPs?

The correct answer is that rigid foam plastic insulation is the type commonly used in Structural Insulated Panels (SIPs). SIPs are designed to provide excellent thermal performance and structural integrity, and rigid foam insulation fits these requirements perfectly. It has a high insulation value, which helps to minimize heat transfer, making buildings more energy-efficient. Rigid foam insulation is also lightweight and has a consistent thickness, which helps achieve the required performance characteristics in SIP construction.

The other types of insulation mentioned are not typically used in SIPs. Polyethylene foam is generally a light and flexible insulation material more suited for applications like packaging or protective wrapping. Fiberglass insulation, while commonly used in traditional wall cavities and attics, does not provide the same level of structural support and thermal performance as rigid foam in the context of SIPs. Spray foam insulation, although it offers good insulation properties, is usually applied on-site and is not used as the core material in prefabricated SIPs, which require a consistent thickness and structural integrity provided by rigid foam.