The thermal stability of chemical vapor deposited (CVD) Parylene N used as a pore sealant has been evaluated. Parylene N pore sealing is shown to have a thermal stability up to 400 degrees C in an Ar-3% H-2 forming gas ambient. A 1 nm thin film of Parylene N remains effective at blocking Co precursor penetration into porous methyl silsesquioxane (MSQ) during the CVD of Co, even after being annealed at temperatures up to 400 degrees C. The leakage current improvement of pore sealed MSQ with an Al electrode is also maintained after a 400 degrees C anneal. In addition, the thermal stability of thin Parylene N films themselves has been verified up to 400 degrees C.