Some of the 9.9's most interesting technology is hidden within the frame. Like all top carbon frames, the Session frame is built using a bladder - a lightweight inflatable balloon is inserted within the frame to apply pressure to the layers of carbon as they cure inside the mold. A rubber bladder cannot apply even pressure to tight and or complex-shaped sections within the frame. According to Trek, instead of adding extra carbon to reinforce these trouble spots, it uses a proprietary low-density, ultra-stiff material inside the frame to evenly pressurize these areas from within. Interestingly, Trek claims that this method, referred to as 'InTension', actually results in tube sections that are four times higher in flexural strength and eight times as stiff. InTension helps build a lighter, stronger carbon structure by replacing inner layers of carbon with a material that fills more volume, but with significantly lighter weight than a carbon-only structure. Presently, the Session 9.9 is the only frame in Trek's lineup that currently uses InTension, but Trek is so pleased with the performance that it is likely to be found on other models in the near future. span style='font-size:13px'>i>Photo by Sterling Lorence/i>/span>