A solar panel backside film used in solar panel constructions. The film comprises a PET film having a net peak area as measured by differential scanning calorimetry of about −15 J/g to about 5 J/g measured from the endpoint of the glass transition (Tg) up to 230° C., and an additive to opacify the PET film. A polymeric layer is adhered to the PET film to create a solar panel backside film. The solar panel backside film generally has a reflectivity of 50% or greater at a point in the visible range of light. Additionally, the solar panel backside film, when applied to a solar panel and exposed to 2000 hours at 85° C. and 85% relative humidity, does not result in exfoliation or visible cracks in the PET film.