DEAR TIM: It's time for a new exterior front door at my house. I love the look of our existing 70 year old wood door, but it never seems to fit right. It's either too tight or too loose. After looking around, I am astonished at the variety of different materials that are now being used to construct doors. Is there any one you prefer? Is there anything I should watch out for? T. I.

DEAR T. I.: I couldn't agree with you more. Exterior door systems have seen tremendous technological breakthroughs in the past 5-10 years. The most appealing doors to me are those that combine several different materials to make a realistic, if not actual, wood door.

Based upon your photo, your existing front door appears to be a 6 panel solid fir door. Solid wood doors can behave in an unruly fashion if not sealed completely. The humidity in the air can make solid wood doors warp and bow, causing them to fit poorly in the frames. My guess is that the top and bottom edges of your door have been neglected. They should have been varnished each time the door was refinished.

There are four primary categories of new exterior doors: steel, fiberglass, composites, and real wood. Believe it or not, the first three categories contain doors, which may be of interest to you.

Steel doors make up a majority exterior door sales in today's market. Steel is dimensionally stable. Humidity will not cause a steel door to warp or twist. You can purchase steel doors that have synthetic wood grained embossed finishes that accept stains. When finished, it is hard to tell these doors from the real thing. Just about every steel exterior door is filled with some type of foam. This foam allows the doors to achieve R-values almost five times that of an ordinary wood door.

Fiberglass entry doors are gaining in popularity. They are very similar to steel doors, however, they tend to be much more resilient. Steel doors can be dented somewhat easily. Many fiberglass doors are also stainable and have rich, realistic wood graining. When finished properly, it is almost impossible to distinguish that the door is not really wood. Fiberglass doors are also insulated with foam and have high R-values.

Some of the most fascinating doors are the composite doors. These doors often take two different materials and blend them together. For instance, one manufacturer uses a composite fiber-reinforced core that is twice as strong as wood. This core will not rot, warp, or twist when subjected to high levels of humidity. This core is then completely surrounded with real wood. The door is actually wood, but yet its not. It offers the beauty of wood, but not the problems.

Last, but not least, are real wood doors. Not all wood doors made today are like their ancestors. Many of the wood doors are made by laminating different, more stable pieces of lumber into a core. This core is then covered with a thin veneer of just about any species of wood you care to have.

Other solid wood doors are manufactured using a cut and turn' method. Different parts of the door start out by using one solid piece of lumber. However, this piece of lumber is often sliced lengthwise into one or more pieces. After being cut, every other piece is rotated 180 degrees and then all the pieces are glued together. This makes the re-solidified' piece of wood much more resistant to warping and bowing.

When shopping for a new door, pay strict attention to finishing instructions. Many of these new doors require specific stains and finishes to achieve good results. Follow directions to the letter. Also, be sure to look for doors that offer adjustable thresholds. These devices allow you to adjust the threshold up or down seasonally, in the event the bottom door sweep fails to contact the threshold for some reason.