Migration of polyisobutylene from polyethylene/polyisobutylene film into foods has been studied in domestic applications such as wrapping of foods and reheating in a microwave oven. The results of these migration studies were obtained by direct measurement using newly developed analytical methods utilizing nuclear magnetic resonance (NMR) and infra‐red (IR) spectroscopy as well as predictively from assessment of loss of polyisobutylene from the film. Total levels of polyisobutylene migration into cheese were found to be 8–10 mg/kg, into cake 1–5 mg/kg, and into sandwiches ranged from < 1 to 4 mg/kg. Reheating foods covered with film in the microwave oven, gave migration levels ranging from <0.01 mg/kg for contact with steam only, up to 0.5 mg/kg for severe splashing of food onto the film and 4 mg/kg for reheated pizza. Migration of polyisobutylene was shown to be skewed towards the low molecular weight fraction of the additive. In typical films, the molecular weight range of polyisobutylene was shown to be 300–6000 daltons (95% limits) centred on 1300 daltons, whereas the additive that had migrated into cheese was found to range from 130–2200 daltons, centred on 520 daltons.