The basic structure of a RTP consists of  a thermoplastic inner layer which is externally wrapped  with a reinforcement material and an outer thermoplastic jacket.  The reinforcement material is the most important layer in the  RTP because it provides strength to the pipe.  Steel,  fibreglass and Aramid fibres are commonly used as reinforcement material.  The other  critical layer in the RTP is the pipe liner which offers low permeability,  low abrasion and a surface that does not promote bonding. Examples of pipe liners include HDPE,  Nylon and  Polyphenylene sulphide (PPS).  Manufacturers usually add other layers to the RTP to enhance thermal properties and inter layer bonding.