The highly-advanced shell on the Luce R5 is constructed with three sections, consisting of a central nylon spine that\\\'s reinforced with carbon fibre and two thermoplastic elastomers. This provides the perfect mix of strength, flexibility and a low weight. Central Cut-out The shell also has a long central cut-out, which Fizik calls its IschialFlex technology and this provides flexible support under the sit bones. It also removes pressure from sensitive areas so you can take on the longest rides and enjoy consistent comfort.