EXPOL ThermaSlab VH Grade for Concrete Floor Insulation

EXPOL ThermaSlab VH is a durable expanded polystyrene insulation solution that achieves R-values above building regulation. 

Designed for applications where high loads are expected, it provides excellent compressive strength under concrete slabs.

Made from environmentally sound expanded polystyrene (EPS), EXPOL ThermaSlab VH protects a building from heat loss through the concrete slab.  The result is a warm, dry, healthy building that costs less to heat and cool.

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Concrete Floor Insulation

A lightweight board, EXPOL ThermaSlab VH is quick and easy to install under concrete slabs. Available in a range of sizes, EXPOL ThermaSlab VH is used where high loads are probable.

For most residential applications, EXPOL ThermaSlab S and H offer a suitable density for concrete underfloor insulation.  For extremely high compressive strength, use EXPOL-X, an extruded polystyrene product.

Other Applications

EXPOL ThermaSlab is also suitable for use in wall insulation, retaining wall insulation, cladding insulation and skillion roof insulation.


Up to 10% of a building’s heat is lost through the concrete slab.  A building insulated with polystyrene under the slab is more comfortable and healthy for occupants.  

EXPOL ThermaSlab is a lightweight polystyrene board that does not compromise on insulation performance.  At a thickness of 50mm, EXPOL ThermaSlab VH delivers an R-value of 1.43.

An exceptionally durable product, EXPOL ThermaSlab does not require maintenance or replacement. Thermal performance, water resistance and compressive strength will last for the life of the building. EXPOL’s expanded polystyrene insulation does not decay or rot and has no nutritional value to termites or rodents.

EXPOL ThermaSlab is easy to cut and comes in a range of sizes making the installation process efficient.  




Once EXPOL ThermaSlab VH is laid, mesh chairs are placed on the board ready for reinforcing mesh. EXPOL supply bar chairs for steel mesh support.



EXPOL ThermaSlab comes in five lengths at 1200mm wide.  Special sizes are available on request.




EXPOL makes insulating easy.  To ensure you get the best result, follow these simple steps.

Installing ThermaSlab VH

Available in a range of lengths, EXPOL ThermaSlab is fast and easy to install. A lightweight product, it is easily moved around the site.  

To install EXPOL ThermaSlab, simply place sheets on top of polythene (DPC) and ensure sheets are not placed under any footings or thickenings for load-bearing walls unless specified by an engineer.

Sheets can be taped together, however, this is not a necessity.  Once sheets are laid, place reinforcing mesh over the top using mesh chairs.

See our Masterspec document for further information.

Technical information



What’s the difference between EXPOL ThermaSlab S/H and EXPOL ThermaSlab VH?

EXPOL ThermaSlab S, H and VH are all excellent choices for concrete floor insulation.  EXPOL ThermaSlab VH is used where very high loads are probable and ThermaSlab S or H are ideal for residential applications.

How strong is EXPOL ThermaSlab?

The unique matrix structure of expanded polystyrene (EPS) creates block rigidity and compressive strength making it an excellent choice for use under concrete floors.  An inert, rigid foam product, EPS holds its shape and does not deteriorate with age.  EPS is often used for commercial applications such as structural base infill as well as road and bridge infrastructures.

Is EXPOL ThermaSlab water resistant?

EXPOL ThermaSlab is virtually unaffected by water, performing better than other foamed plastic products on the market.  Tests on EPS board retrieved after 30 years underground showed less than 1% water content.  Tests taken on EPS board periodically submerged over the same period of time showed less than 4% water content.  

Does EXPOL ThermaSlab VH come in a range of sizes?

Yes.  EXPOL ThermaSlab VH is available in lengths of 2400mm, 2450mm, 2700mm, 3600mm and 4800mm at a width of 1200mm.  It is also available in other widths upon request.

Is EXPOL ThermaSlab environmentally friendly?

Made from 98% trapped air, EXPOL ThermaSlab requires very little raw material for manufacture making it so efficient that it will save up to 200 times its own resource in energy savings.  All EXPOL expanded polystyrene (EPS) products are 100% recyclable.  EXPOL runs one of New Zealand’s largest EPS recycling plant.


EXPOL UnderFloor is available at a number of leading building products stores. Find your nearest stockist here.

View Expol Distributors in a larger map

Other Concrete Floor Insulation products which may be of interest

EXPOL ThermaSlab S and H Grades


EXPOLl Platinum Board

EXPOL-X Edging

Fast Facts
  • A thin, lightweight board, EXPOL ThermaSlab VH is easy to install by a tradesman or handyman.
  • EXPOL ThermaSlab VH is the best choice where high loads are expected.
  • Made of 98% air, EPS does not settle over time, thus ensuring the R-value for the life of the building.
  • Resistant to decay, water and compression, EXPOL ThermaSlab VH does not require maintenance.
  • Underfloor insulation significantly improves the energy efficiency of a home requiring less resources for heating and cooling.
  • EXPOL manufactures EXPOL ThermaSlab polystyrene boards throughout New Zealand, ensuring quick and easy delivery to site.

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Enquiry Form

General Enquiry

Tel: +64 (9) 634 3449

Free Phone: 0800 86 33 73


105 Captain Springs Rd., Onehunga, Auckland

Tel: +64 (9) 634 3449

Free Phone: 0800 86 33 73


105 Captain Springs Rd., Onehunga, Auckland

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