Replacement windows and doors used to be available in grey aluminium if you didn't want wood and the styles rarely improved the aesthetics of the buildings they adorned. Consequently, we are left with a legacy of spoiled period homes which in some cases constitute a fire hazard because windows were designed without large enough opening sashes to escape through.

And then they became available in white PVCu which were initially cheap and of poor quality and poor design but which went on to become the excellent quality they are today and designed to suit the house - not the pocket. As the old-fashioned designs become obsolete, home owners now have a plethora of window and door styles and materials to choose from. The majority of products' enhancements reach a plateau at some point when the essentially ideal has been achieved and what follows are simply tweaks. As with all home improvement products, doors are no exception.

For many years, there has been a very big market for patio doors, which offer convenience and allow light and air into a home whilst providing a highly effective thermal barrier when closed. This market is still buoyant and the products will continue to be installed successfully in homes where economics or taste insist, but fairly recent developments in this market looks to have found us at that plateau where doors are concerned. Patio doors have recently made way for the "Rolls Royce" in this market which is now the hugely flexible bifolding door. Anyone looking to buy patio doors now should first be considering whether they could increase their investment to a bifolding door.

Bifold doors can be configured to span a very wide aperture or smaller spaces, behaving when closed as a glass wall to allow in increased light and to provide panoramic views over the outside vista or garden. They can very easily open up an entire wall to allow seamless integration of external and internal areas, for example, for parties or for children to play safely inside and outside on a lovely day. Alternatively, they can serve to expand available space in restricted areas, such as allowing inclusion of a balcony to form part of a small apartment on a clement day or lightening up an otherwise dark corner.

Fully opened, the doors concertina and store compactly to left, right or both sides to limit their intrusion. They can be configured to provide french style doors when full opening is not required and a single opening door for pedestrian access in the normal way.

Available in most modern materials, including timber, aluminium, PVCu and aluminium clad timber, this product is available in a wide range of colours and finishes from specialist window companies. It is particularly attractive in aluminium clad timber where the choice of colour on the maintenance-free aluminium outside can complement your home's exterior whilst the beauty and warmth of wood can enhance any interior.

A not insignificant investment, this product should last, trouble free, for very many years. It is essential to ensure that your supplier can offer all of the many security features available for bifold doors which make them a high security option, suitable for commercial use by garages displaying high worth cars and restaurants alike. The manufacturer should use only a top quality sliding mechanism for guaranteed trouble free use and should offer the widest range of materials and finishes to ensure you are happy with your investment for many years to come. As a new product, not all door manufacturers can offer these and consumers should be prepared to shop around and ensure that they buy the best quality from a reputable manufacturer.