Although most of the emphasis on fuel conservation for the home has been placed on the need for adding insulation, experts in this field have become increasingly aware that cold air infiltration is often responsible for just as much heat loss as inadequate insulation.

The most common source of cold air infiltration is loose-fitting windows and doors -- but his can almost always be cured by installing weather stripping around every window and door opens to the outside. Fortunately, there are a number of new and improved types that are easier than ever for the do-it-yourselfer to install (most have adhesive backing and require no tools other than scissors or knife). They are made of durable and maintenance-free, flexible plastic and will, in many cases, do a better job than conventional types of do-it-yourself weather stripping.

In addition to the many existing good-quality, weather-stripping materials, such as adhesive-backed foam strips, foam-faced rigid metal and wood strips, felt, and adhesive-backed tapes, two large companies -- 3M and Stanley Hardware -- have come out with some completely new, efficient and easy-to-install types that will often solve problems that could not be corrected by other materials.

The 3M Company's new weather-stripping material is designed for use on windows and doors. Made of flexible polyprene plastic, it comes in rolls and is available in white or brown. The strips are just under one inch wide and have a crease or "hinge" down the middle so that after being being cut to length, they can be easily folded lengthwise to form a hingelike V-shape.

This material, called 3M Adhesive Weather Strip, is designed so that the one loose edge (that has no adhesive) presses against the edge of the door or window to permanently seal out drafts. You can apply these strips around doors, as well as along the top, bottom and sides of sliding sash frames. In each case you cut the strip to length with scissors, then fold it down the center to form the V-shape.

Press it into place (after peeling off the protective paper on the adhesive side), so that the opening of the V faces toward the outside. The free or springy side of the V will then press against the door or window frame to fill any gaps that remain when the door or window is closed. Because the adhesive will stick even in sub-zero temperatures, the stripping can be applied on the coldest days. The material comes in 17-foot rolls and costs about $5; 60-yard rolls are also available.

Unlike 3M, Stanley Hardware has entered the field with a complete line of assorted weather stripping. Some are the traditional types (self-adhesive foam strips, metal and plastic door-bottom strips, rigid metal and wood moldings with flexible vinyl facings, etc.), and several are new designs that are permanent, efficient, and easy to install using only scissors.

To seal doors, Stanley has introduced two new styles of plastic weather stripping -- both with self-adhesive backings, and both designed to be invisible when the door is closed (like the 3M material described above.) These also have springy "fins" or edges that press against the edge of the door (single fin. No. V1313)8 or against both the face and the edge of the door (double fin. No. V1314).

Both come in brown or white, and both have adhesive backing on two sides of the semirigid corner moldings so that they stick to the door frame as well as to the inside face of the stop molding.

The single-fin model is for doors with gaps of up to 1/4 inch; the double-fin model is for doors with larger gaps of up to 3/8 inch.

Each of these Self-Stick Door Weather Seals comes packaged in sets that contain enough material to seal an average door, at a cost of $7.99 for the double-fin set and $5.99 for the single-fin set.

Stanley also makes two new types of window weather stripping -- one for double-hung windows, and one for casement (hinged) windows. The one for double-hung windows, No. 1338 Window Weather Seal, comes in white or brown and is unusual in that it is not actually fastened in place by adhesive, or by fasterners of any other kind.

It consists of a T-shaped strip that is simply pressed into place and left there for the winter. One of the three fins of the T is pressed into the joint between the face of the sash and the edge of the stop molding -- the other two fins then spread out and press against the inside face of the sash and the stop molding to create an airtight seal that will also prevent rattling. A package containing enough material for a typical window costs $5.99.

For hinged windows Stanley makes a special self-sticking plastic stripping that has a soft, compressible bead along one edge. Also made in white and brown, and designed so that it is completely concealed when the window is closed, No. 1331 Hinged Weather Seal Provides a simple but efficient means of sealing air leaks without using bulky materials that are visible on the inside. This material is installed on the inside face of the hinged sash so the bead presses against the frame when the window is tightly closed. It comes in 18-foot rolls and costs $4.79.

Stanley is also marketing Replacement Weather Seals for storm windows (No. 1330) and storm doors (No. 1329). They can be used to replace the original pile-like yarn after it has become badly worn or shrunken. The window seal material comes in a 40-foot roll ($5.990, and the door seal comes in a 30-foot roll ($6.99).

In addition to these fairly new types of weather stripping, the company has also put out some improved versions of olfer types. There is a 3/8-inch-square self-stick foam stripping that has vinyl covering that keeps it from absorbing water; and a closed-cell, self-sticking, ribbed rubber stripping that compresses more easily than conventional foam or rubber. The ribbed material comes in two sizes: 1/8x3/8x1/16 inch, and in both white and gray. The vinyl-clad foam costs $3.99 for a 10-foot roll; the ribbed rubber cost $3.99 for a 10-foot roll of the larger material, or a 17-foot roll of the smaller-size material.