What is used to prevent heat migration to the underground soil in slab on grade hydronic heating systems

4-mil polyethylene is primarily used as a vapor barrier rather than an insulator. While it can prevent moisture from penetrating the slab, it does not provide significant thermal resistance. Thus, it is not effective in preventing heat migration compared to materials specifically designed for insulation.

1/4-inch polyvinyl sheeting may offer some insulation properties, but it is generally too thin to provide adequate thermal resistance for slab on grade systems. Its primary role is more aligned with moisture protection than with heat retention, making it insufficient for preventing heat loss effectively.

Foil-backed corrugated sleeves are used in specific applications, such as insulating pipes, but they lack the solid structural qualities and thermal performance needed for slab insulation. Their design does not offer the continuous thermal barrier required to effectively prevent heat migration in slab on grade systems.