• Fiberglass patio doors are durable and attractive but have some problems.Waterfront Patio image by wabkmiami from Fotolia.com
  
  Fiberglass is an attractive, low maintenance and durable choice for patio doors that is quickly replacing traditional wood patio doors. Fiberglass is resistant to rust and mold and will not deteriorate upon exposure to the environment. A fiberglass door is made by molding fiber skin with wood grain and wrapping it around an insulating core--typically urethane. Fiberglass doors are available in various designs and complement all types of facades. Fiberglass patio doors, however, have some problems to assess before purchase.
  
  

Costly

• Fiberglass patio doors have high purchasing costs and are not financially feasible for most middle-class homeowners. The simplest varieties typically cost upward of $500 as of September 2010. More elaborate designs and frames easily exceed $3000, according to the House of Windows. Fiberglass patio doors also require professional installation, owing to warranty specifications. Professional installation is costly and can run into hundreds of dollars. The doors are not entirely maintenance free either. They often need sealing and periodic staining on their sides.
  
  

Limited

• Most fiberglass patio doors are available in a limited number of sizes. Large fiberglass doors cannot be cut, planed or sanded down and homeowners may need to adjust the size of their door frames instead to accommodate them perfectly. Fiberglass patio doors cannot be customized, and most manufacturers offer fixed styles and dimensions, according to Sheri Koones in the book "House About It." They are not easy to modify to add hardware such as deadbolts. Fiberglass is a relative newcomer to the door market, and fiberglass patio doors are not as readily available as their wood and steel counterparts.
  
  

Discoloration and Damage

• Most fiberglass patio door manufacturers tout the fact that their products will not rot, check, warp, split or crack. However, according to a book published by Taunton Press titled "Doors," fiberglass doors are susceptible to thermal bowing in regions with great temperature fluctuations. Thermal bowing is when the inner surfaces of a door expand more than the outer surfaces, inducing the door to bend, causing structural damage to the door and reducing the door's thermal performance. Stained fiberglass patio doors are susceptible to discoloration by insecticides and solvents, such as turpentine. They are susceptible to scraping and scratches by sharp objects. Home cats, for instance, are liable to scratch and ruin fiberglass patio doors in an effort to get outdoors.
  
  

Inefficient Insulation

• Not all fiberglass doors incorporate insulating urethane or polyurethane cores. Those without additional insulation are less energy efficient than aluminum and steel patio doors. Completely sealing fiberglass patio doors against air infiltration is difficult. Additional airtight insulation is both ineffective in the long run and costly.