Enhanced EPS

Epsitherm Graphite Enhanced Polystyrene Insulation

Wetherby’s Enhanced EPS Insulation comprises of expanded beads of polystyrene that incorporate a graphite component, fused together in a pressurised steam-heated mould. The addition of graphite provides a significantly improved thermal insulation material.

Wetherby’s Enhanced EPS Insulation is produced to the requirements of ‘BS EN 13163 Thermal Insulation
Products for Buildings – Factory Made Products of Expanded Polystyrene (EPS)’ specification.

BBA Approved


Although Wetherby Enahnced EPS Insulation has significant resistance to the passage of water vapour, it should not be regarded as a damp-proof membrane or vapour-control layer and will not provide a barrier against damp penetration. A suitable damp-proof membrane or vapour-control layer will be required in most forms of construction – see individual product and application data.

Moisture Properties

Water vapour diffusion resistance factor μ 20-40
Water vapour permeability _ mg/(Pa.h.m) 0.018-0.036
Vapour resistivity (MNs/gm) 145

Fire Properties

In common with all organic materials, EPS is combustible. However, provided it is specified and installed correctly, in accordance with the manufacturer’s instructions and BS 6203 guidance, it will not present any undue fire hazard. The standard recommends that for all applications, the material should be protected by either a laminated facing layer, or fully enclosed by the form of construction. Class E ‘flame-retardant’ additive material reduces the rate of flame spread but should not be considered as offering enhanced fire performance. EPS is ‘combustible’ as defined in BS 476: Part 4. When burning, EPS behaves like other hydrocarbons such as wood and paper. Class E material products of uncontrolled combustion are carbon monoxide, carbon dioxide, styrene, hydrogen bromide and water vapour; the decomposing styrene will give off a certain amount of dense black soot. Flash ignition temperature is between 350°C and 490°C depending on the application and the exact circumstances of use. Under certain circumstances the material can be readily ignited by a naked flame but providing it is correctly installed, this does not present any disadvantage in use.

Biological Properties

EpsiTherm Insulation will not sustain mould growth, and has no nutrient value to insects or vermin. The material is non-biodegradable and care should be taken to dispose of waste and off cuts at a licensed waste site.

Thermal Properties

Coefficient of linear expansion: 0.6 x 10-6ºC.
The material is sufficiently resilient and flexible that no allowance needs to be made for thermal expansion in the method of insulation.

Thermal Performance

Thermal conductivity: 0.032W/mK
Thermal resistance: 31.25mK/W

Working temperature range

Enhanced EPS Insulation can be used within the temperature range -150ºC to +80ºC.

Compressive Strength

Compressive strength @ 10% compression (kPa) 70
Compressive strength @ 1% nominal strain (kPa) 20
Bending strength (kPa) 115

Compatibility with other materials

EPS is soluble in aromatic, halogenated solvents and ketones; it should be protected from contact with hydrocarbons and strong solvents using a suitable membrane. EPS should not be permitted to come into contact with PVC-sheathed electrical cables since this will lead to migration of plasticiser from the PVC resulting in embrittlement of the cable sheath. Cables should be protected by the use of a physical barrier, for example by being enclosed in a conduit or by an air gap.

Health, Safety and Environment

EPS is non-toxic and biologically inert. It is not irritating to the eyes or skin and no medical treatment or action is required as a result of accidental ingestion. No special precautions are required during handling or cutting when carried out in well-ventilated areas. The volume of EPS boards is 98% air. In polystyrene, styrene monomer, shown to be safe in use, constitutes a maximum of 0.1% by weight of the product. This minute trace of styrene monomer constitutes no threat to health. The expanding agent, pentane is a saturated hydrocarbon and is non-toxic and constitutes no threat to the ozone layer. EPS, Class E, flame-retardant additive material, contains around 0.5% of the flame retardant hexa-bromocyclododecane (HBCD) which is entrapped in the polymer matrix of the EPS.


Store Enhanced EPS Insulation boards under cover, protected from high winds and out and out of direct sunlight. Care should be taken in storage not to bring the boards into contact with highly flammable materials such as paint, solvent or petroleum products. Smoking should be prohibited in the storage area and the products must not be exposed to flame or other ignition source.


In accordance with BS EN 13163 tolerances on the cut dimensions are defined as follows:
Length: ±3mm or ±0.6% whichever is greater (L1)
Width: ±3mm or ±0.6% whichever is greater (W1)
Thickness: ±2mm (T1)

Squareness: ±5mm per 1000mm (S1).
Alternative tolerances can be provided for specific applications.

Dimensional stability: ±0.5% under constant laboratory conditions (DS(N)5)

(all figures quoted are based on 70mm boards)