Abstract: This document describes electromagnetic radiation (EMR) transmissive polymer substrates and techniques for producing EMR transmissive polymer substrates by pre-treating polymer substrates with at least one lipid. In aspects, the EMR transmissive polymer substrates are infrared (IR) transmissive polymer substrates and the techniques described are for producing IR transmissive polymer substrates. In general, disclosed techniques include applying a coating of at least one lipid to at least one surface of a polymer substrate and then performing a heat-treatment process on the coated polymer substrate. The techniques may also include performing a cooling process on the polymer substrate after the heat-treatment process.