Nylon 12 resins have been utilized for liquid fuel lines in automobiles for more than 25 years. This resin has proven its suitability in monowall tubing in the chassis environment and in contact with normal fuels. The development of more aggressive fuels (mostly those containing alcohol) and the establishment of new hydrocarbon emission standards by various government agencies have changed this.
In response to the changing situation, multilayer tubing has been developed in order to improve the properties of the nylon 12 tubing, primarily the permeation resistance. Hüls has developed two different constructions, both of which contain a fuel-resistant barrier layer in the wall of the Nylon 12 tubing. One utilizes a barrier layer of a specialty polyester resin with good bonding to the outside and interior layers of Nylon 12 without use of an adhesive. The other utilizes a PVDF resin bonded to the Nylon 12 by an adhesive layer. The results of the addition of these barrier layers are a 10 to 20 fold improvement in permeation resistance compared to Nylon 12 monowall tubing.