What was found
FLT 635 AIR TURNBACK AFTER F/A''S REPORTED STRONG SMELL OF SMOKE IN CABIN. ON DESCENT F/A''S REPORTED SMELL RETURNED. PRIOR TO LIFTOFF CAPT NOTICED A MYLAR BALLOON DRIFT BY HIS WINDOW. C/C INSPECTED INLET AND EXHAUST ON RT AND LT ENGS AND FOUND MYLAR BALLOON IN RT INLET. REMOVED SAME, CHECKED AND SVC LT AND RT ACM, CHECKED 8 AND 13 STAGE DOMES. NO OIL FOUND. CLEANED APU INLET DOOR, REPLACED LT AND RT WATER SEPARATOR BAGS. RAN ENGS PER PFHB WITH PACKS ON, ALL NORMAL AND NO SMELL NOTED.