Evolution Of Elastomeric Felts

Traditional Felts
Historically, flat roofs were constructed using traditional bitumen based felts (B.S.747)

These felts have very little elasticity, and become brittle with age. This has been made worse over recent years due to the increased use of high insulation materials under these felts, which increases the roof movement through temperature changes.- especially between the hot days of summer, and the recent freezing temperatures of winter.

H.T. or 'High Tensile Felts
To overcome these basic problems, the designers added stronger reinforcement to the felt. Using mainly polyester, which is extremely strong and has the added benefit of resisting piercing. Unfortunately, however strong these materials are, they are limited in their durability by using a base material from oxidised bitumens, and are therefore still subject to the same deterioration when subjected to huge temperature ranges.

Elastomeric Felts
The vastly altering building market, left the designers with two main problems to overcome;
1. Designing a material which is truly flexible and retains this flexibility throughout all temperature ranges.
2. Designing a material which has a longer life expectancy and retains the traditional methods
of fixing.

After years of development, it was found that by adding polymers (SBS) to the bitumen in the manufacturing process, this resulted in a felt which is capable of accommodating repeated thermal movement, without any deterioration, and hence the life expectancy of the material is greatly increased.