A research project to develop and optimize a transparent insulation (TI) structure based on commercially available films showed, that in addition to poly(carbonate) (PC) and poly(methylmethacrylate) (PMMA) other amorphous and semicrystalline polymers such as cellulose triacetate (CTA) and poly(ethyleneterephthalate) (PET) exhibit favorable property profiles for application in low temperature systems (e.g. TI wall systems). Investigations were carried out in order to study the influence of time, temperature, humidity and solar radiation on the solar and infrared performance properties of various polymer films. Whereas the infrared properties are only slightly influenced after exposure to elevated temperatures, humidity and solar radiation, in the solar range especially extinction due to scattering increases. Detailed results are presented in the paper for four polymer film types and for TI structures made thereof. Furthermore, the results are interpreted in terms of both the molecular and supermolecular structure of the polymer films. Besides PC and PMMA films, PET and CTA films show an interesting long-term performance, being an interesting alternative to the more expensive PC and PMMA polymers. (c) 2005 Elsevier Ltd. All rights reserved.