The thermal decomposition of fluorinated single-walled carbon nanotubes (F-SWNTs), known to result in pristine SWNTs, has been investigated by freezing the gaseous products formed at temperatures between 50 and 500 degrees C under high vacuum in an argon matrix at 10-20 K and analyzing the trapped species by IR spectroscopy. The major products of F-SWNT decomposition are carbonyl fluoride (COF2) below 300 degrees C and CF4 above 300 degrees C. For comparison, graphite fluoride is stable thermally up to 300 degrees C under these conditions, and the major gas-phase species at temperatures below 500 degrees C are CF4 and the CF3 radical. F-SWNTs are thermally less stable than graphite fluoride, and etching of the nanotubes is observed at lower thermolysis temperatures.