Atmospheric pressure non-equilibrium plasma (APNEP) has been developed in the UK by EA Technology Ltd and is currently being investigated in a joint project with the University of Surrey. APNEP has been used to induce surface modification changes on commodity polymers such as high density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP), poly(ethylene terephthalate) (PET) and poly(methyl methacrylate) (PMMA). A stable atmospheric pressure glow discharge can be formed with a variety of gases, (e.g., nitrogen, air, argon and helium). In all cases, the plasmas are capable of inducing surface modification of commodity polymers in the near-field and remote afterglow regions. However, as APNEP can have a significant thermal component, care must be taken to avoid thermal decomposition of the polymers. This study has used differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) to investigate the thermally induced transitions and thermal decomposition behaviour of commercial polymers. The DSC measurements give melting points, heats of fusion and crystallinities. TGA has been used to measure the onset of thermal degradation in both air and nitrogen atmospheres. In parallel with these experiments, temperature profiles of the downstream region of APNEP have been recorded. As a result, positioning of samples and residence times to avoid thermal damage to the substrates can now be achieved.