Substrates suitable for use in a touch sensor are described. In some cases, the substrates include an inner layer and first and second heat-set polymeric outer layers. The first and second outer layers each have an in-plane birefringence of less than 0.1. The inner layer is substantially uniaxially birefringent and has an in-plane birefringence greater than 0.01. In some cases, a substrate includes a block copolymer which includes a first polyester and second polyester. The first polyester has a melting point greater than 200 ° C., and the second polyester having a melting point less than 200° C. The block copolymer includes the second polyester at 50 to 80 percent by weight. The substrate is substantially uniaxially birefringent and has an in-plane birefringence between 0.001 and 0.1.