A new type of polyester fibre is being brought into production by Shell Chemicals predominately for the residential and industrial carpet markets. This fibre has the tradename of Corterra7 and is a poly(trimethylene terephthalate) (PTT). These fibres have a number of traits that lend themselves to carpet products. Shell expects to produce 400 million pounds of Corterra7 polymers for the general marketplace by the end of the third quarter of 1999 and, thus, it will begin to appear as evidence in cases. PTT fibres have many similarities to, but some important differences from, the more common poly(ethelyene terephthalate) (PET) fibres. The history of PTT, its optical and instrumental characteristics, and data from known samples are presented in this technical note.