PURPOSE: Fiber sheets are impregnated or coated with a polyurethane containing a specific spiro compound to improve the prevention of yellowing caused by NOx and pinking caused by exhausting gases from vehicles.

CONSTITUTION: Fiber sheets are impregnated and/or coated with a polyurethane containing a compound of the formula (K is H, benzyl; R1WR5 are H, hydrocar- byl) or its derivative. The fiber sheets mean knitted, woven and nonwoven fabrics and fibers forming these fabrics are preferably extremely fine as less than 0.3 denier. The compound of the formula is, e.g., 1,3,8-triaza-8-benzyl-7,7,9,9-tetramethyl-3-octyl-spiro[4,5]-decane-2,4-dioene.