Below Grade



Below Grade Rigid Applications
For exceptional, long-lasting performance in below grade applications, no EPS or XPS competitive product digs deeper than ThermalStar® X-Grade.® With its outstanding thermal and physical properties, durable ThermalStar X-Grade protects foundation walls during backfilling, while providing excellent insulating performance. Patent pending integrated termite resistance assures peace of mind.



It’s Orange or It’s Ordinary®

What sets ThermalStar X-Grade rigid insulation apart? Outstanding performance and exceptional value. ThermalStar X-Grade rigid insulation maintains its superior thermal and mechanical properties over time — including R-value and moisture resistance — to provide long-term stability and protect your installation for years to come.

An excellent value when compared to other rigid insulation products! For performance you can trust and value you’ll appreciate, specify ThermalStar rigid insulation for your next project.

Long-Lasting Thermal Performance
ThermalStar X-Grade has been proven to absorb minimal moisture. Also, unlike other insulation products, ThermalStar X-Grade is a “breathable” material. This breathability ensures long-term performance. In fact, a 15-year comparative study of actual field applications of below grade insulation confirms the R-value is retained.

Integrated Termite Resistance
Termites can do serious damage to untreated building materials. With ThermalStar X-Grade, a proven termiticide is integrated into the chemistry of the product and is not a surface coating. US building code requires that rigid foam demonstrate resistance against termite attack when used below grade. In many states, X-Grade is approved for this use — see ICC-ES Evaluation Report (.pdf).


ThermalStar below grade products for vertical on foundation walls and under slab applications are available in a range of compressive strength grades and standard and custom sizes.

X-Grade 15, 25, 40, 60 (below grade insulation) — Vertical on foundation walls, under slab applications:

  • Typical size is 4′x8′, other sizes are available upon request, including 4′x4′, 2′x8′, 4′x9′ and 4′x10′
  • Thicknesses available from 1/2″ to 32″
  • Products between 1″ and 3-1/2″ are scored for easy snapping into 16″ and 24″ wide panels


pdficon_small ThermalStar X-Grade Sell Sheet

pdficon_small ThermalStar X-Grade Product Information Sheet

pdficon_small ThermalStar X-Grade Physical Properties

pdficon_small ThermalStar X-Grade Rigid Polystyrene R-10 Comparison Sheet

pdficon_small ThermalStar X-Grade Canadian Product Information Sheet

pdficon_small ThermalStar X-Grade Canadian Rigid Polystyrene R-10 Comparison Sheet

pdficon_small ThermalStar X-Grade Substitution Request

pdficon_small Technical Bulletin 104: Drying Potential

pdficon_small Technical Bulletin 105: Water Absorption & R-value Retention