Therefore silicone rubber is increasingly being used as the soft component in many applications due to its excellent properties. LSR can be used even at high temperatures and is characterised by outstanding electrical properties, a high level of resistance to many chemicals and a high level of aging stability. In order to achieve a permanent bonding of the thermoplast and silicone components for the two component parts, interlocking compounds are mainly used. Another option is to apply a bonding agent to the thermoplast preforms, which can produce a chemical compound of both materials. However in this case fully-automatic production is hardly possible as the process has to be interrupted to apply the bonding agent. In contrast, adhesion-modified silicone types, which already contain a bonding agent, allow uninterrupted operation.

With chemical compounds, mechanical anchoring of the soft component, for example through undercuts or perforations, is not needed, thus simplifying the designing of parts and moulds in many cases. Partner components for silicone with respect to bonding include PA, polyester, PBT, and PPS.

The combination of thermoplast and liquid silicone processing demands a sophisticated mould design. Particular attention must be given to temperature control - at high temperatures LSR cross-links in the mould whereas a much lower temperature level is needed on the thermoplast sections. In some cases each section of the mould must therefore be separated from one another by means of insulation.