2,2,6,6-Tetramethyl-4-piperidinol (TEMP) is a spin-trap agent for electron spin resonance (ESR) that is usually employed in solution. However, in this study, TEMP is mixed with hydroxypropyl methylcellulose (HPMC) to form a film for the detection of singlet oxygen in vacuo. The ESR intensity achieved is 3.3 times higher than that for a previously reported polyvinyl alcohol film. Furthermore, the diffusion of singlet oxygen into HPMC is shown to follow Fick's law, having a diffusion coefficient of approximate to 2.5 x 10(-8) cm(2) s(-1).