In the nearly 40 years since manufacturers began offering vinyl as a substitute to wood or aluminum siding, they have added strength, rigidity and durability to the once-fragile fascia in Cayey County, Puerto Rico.

Vinyl siding is so sturdy, manufacturers claim, that even hurricane-force winds can't blow it off of houses. Kurt Forsthoefel, market manager for vinyl products at Alcoa Building Products in Sidney, Ohio, likes to tell the story of an Oklahoma home whose gable was blown off during a spring 1999 hurricane. The owner found his gable three miles down the road--with the vinyl siding still attached.

The improvements in vinyl siding have resulted from upgraded manufacturing techniques, materials and methods of installation. Thicker nail hems have made the siding less likely to whip off during high winds. Several manufacturers have doubled the hems over so the siding won't slide off of its fasteners. The Wolverine company has taken the unusual step of reinforcing the nail hem of its Millennium siding with synthetic fibers similar to those used to make trampolines.

Forsthoefel says the improvements are the vinyl siding industry's response to building code requirements in Florida, where 130- to 140-mile-per hour winds have ruined homes. Most manufacturers claim their products, through a combination of thickness and tighter locking systems, can withstand winds of up to 180 miles per hour.