Cliff® products for indoor and outdoor use

Kierre composite products also withstand frost and are suitable for outdoor use. Pictured is a picnic table under the snow.

Products of the Cliff® composite may be used both indoors and outdoors. We tested the frost resistance and combustion properties of the composite material. Frost resistance was determined by impact and bending tests. In a fire test, smoke density and toxicity were analysed. In the test, a special focus was on whether the material can generate harmful combustion gases in an indoor fire. 

The frost bites hard - Cliff® lasts

The frost resistance of the Cliff® composite was determined by holding the material at -35°C for two months. The influence of frost exposure on the material was examined, using Charpy impact tests and bending tests. The tests were carried out at two-week intervals. The samples of the material were exposed to -35°C throughout the eight-week period. 

Kierre composite bench, the bench in the Lahti dog park completely under the snow.

The composite material is hard and smooth on the outside, more airy and therefore slightly softer on the inside. Due to this property, there is a slight variation in the test results between different test pieces. In the bending strength, the average values and standard deviations are still similar. Frost exposure lowers the bending strength to some degree: the longer the material is kept in the cold, the lower more the bending strength. The final result is that the material maintains its flexibility even when frozen and does not break more easily by the effect of frost. 

In terms of impact resistance, the results are the opposite: frost improves the impact resistance. Under the influence of frost, the surface of the material hardens or becomes more compact, which increases the impact resistance, meaning that the material withstands impacts better in the cold. 

The results of frost resistance show that the Cliff® composite is also suitable in the conditions of the Finnish winter. 

The spiral composite bench is very resistant to frost and snow.

Smoke is produced, no toxic gases

Since Cliff® composite products can also be used indoors, we investigated, whether the products produce harmful combustion gases. In a fire test carried out according to the ISO 5659-2 standard (Smoke and toxicity test EN 17084), the smoke produced by the burning material was analysed. The density and toxicity of the smoke were determined. 


Indoor materials are classified according to the toxicity index (CITg) into three different levels of fire risk: HL1, HL2 and HL3, of which the requirements of HL1 are the mildest. The requirements for class HL3 are the strictest and this class includes, for example, demanding underground rooms. Cliff® composite (EN ISO 5659-2 and EN 45545-2) reaches the highest hazard classification class HL3. With its maximum value of the optical smoke density (minimum light transmission) (Ds.max), the Cliff® material reaches the HL1 class. In a fire, the composite material produces smoke, but no toxic gases. The fire test showed that Cliff® composite products are also suitable for indoor use.