Thermal Properties of EPS

The composition of EPS – it is 98 per cent air and is formed of a closed-cell foam structure consisting of microscopically small air bubbles – makes it the simplest and lowest cost thermal insulator compared to other commonly used packaging materials.

The average thermal conductivity of EPS is 0.038 W/mK at 15g/l density.

EPS offers totally reliable insulation because its strength and insulation properties are unaffected by wet or damp conditions and it does not become brittle in low temperatures.

Leading food companies use EPS boxes to keep fish fresh and safe for consumption, to deliver food over the Internet and to package other perishable items.

Drug companies select EPS to package pharmaceutical products that require a secure cold chain during transit. Its hygienic appearance, protective abilities and lightweight character also recommend the material to this sector.

EPS can safely be used in conjunction with ice or other coolant devices to extend the time period in which it can maintain low temperatures. In this context EPS packaging can be tested in special chambers designed to mimic temperature changes over several days, allowing for temperature drops at night. In this way, any design alterations that are required, can be made to ensure that temperature sensitive items such as vaccines or live medicines arrive in a condition that is safe to use.

The insulating properties of an EPS pack can be augmented by:

  • Increasing the thickness of the package wall.

  • Reducing the internal surface area by designing the pack to fit tightly around the product.

  • Increasing the bulk density of EPS up to 28 gms per litre, after which, there is no additional benefit to further increasing the density.

  • Ensuring the connections between the upper and lower parts of the pack are airtight by designing well-fitting tongue and groove joints.

  • Controlling air circulation in the pack by inbuilt internal ribs. Your manufacturer of EPS packaging will be able to advise you on designing an EPS pack to meet your insulation requirements.

Thermal conductivity of some conventional packaging materials

EPS Expanded Polystyrene packaging - Average tensile strength, kPa