Ptfe sheets. Cheap and easy to cut to whatever size and shape you need. https://www.amazon.com/gp/aw/d/B018YMFIT8/ref=mp_s_a_1_2?ie=UTF8&qid=1506342360&sr=8-2&pi=AC_SX236_SY340_FMwebp_QL65&keywords=ptfe+roll