If you're planning to pour a concrete driveway, sidewalk or a patio this summer, use FlexxBoard25 foam board insulation. Two-inch 4-by-8 sheets of high density FlexxBoard 25 insulate concrete slabs to protect from frost expansion and cracking. FlexxBoard25 increases the life and structural integrity of concrete for exterior and interior applications. In addition to exterior concrete slabs, such as driveways, sidewalks and patios, some interior applications for FlexxBoard25 include concrete slabs for basements, structural fill, shop/garage slabs and concrete floors.