Like death and taxes, changeable weather happens. If you are out pushing the aerobic limits, keeping comfortable can be a challenge, unless you understand the finer points of layering. The theory behind layering suggests that as your body temperature fluctuates or the weather shifts, you simply peel off or add available layers as needed. Simple? Well...it used to be until manufacturers introduced so many confounded layer thicknesses and fabric weaves to the mix. Like a set of Ginsu knives, some of these wild fabric concoctions will do just about anything including shed wind, wick away moisture, keep you warm, keep you cool and even dice a carrot--well, maybe that's stretching it, but not by much

While the basic concept of beginning with a base layer, then adding insulative layers as needed and topping it all off with a protective layer to shed wind and rain still holds, the lines between the categories have definitely become fuzzy.

Where underwear ends and outerwear begins is no longer clear. Today's designs go both ways just as easily. With all the different blends of synthetic fibers and fabrics, as well as different weights (most common are lightweight, mid-weight, expedition weight), the aerobically inclined can turn to one, two or more layers of underwear to accomplish their layering needs. Some creative weaves and constructions even offer wind-stopping properties, usually sewn or woven into the front panels--ideal for sports such as skiing and mountain biking when speed and wind can accelerate thermal loss and lead to chilling.

Bicomponent knits, polyester / cotton blends work to provide wicking and insulative properties in one layer--the side facing your skin is water-hating with the side away from your skin being water-loving and pulling moisture through. You'll stay dry and happy, even with only one layer on, something not possible with old single-function weaves.

Stretch fleece and microdenier pile provide cross-over applications too, working equally well as base layers or for around-town sweaters or functional insulative add-ons for cross-training needs. I love microdenier pile as it can be worn alone or layered under or over other pieces and it has excellent wicking capability as well as more windproof potential than basic expedition weight layers.

Even that most important of fabrics to runners and bladers, Lycra tights, has not been immune from weaving and designer wizardry. Product names such as Therma Fleece, Drylete, Dry-Fit and Ultrasensor (it used to be Fieldsensor) combine Lycra with moisture-wicking synthetics that offer thermal properties.

In putting together your "ideal layering system" there are some general considerations. What you are seeking to do is create a system that effectively combines elements of breathability, wicking, rapid drying, insulation, durability, wind-resistance and water-repellence while still being lightweight and offering the necessary freedom of movement--all with just a few garments. What particular articles of clothing you choose on a particular day will depend on your intended aerobic level and the anticipated weather conditions.

As you know, the basic intent of a base layer is to manage moisture. Your base layer will be first article of clothing you put on, and the last to come off. Since your own skin will be churning out the perspiration, the goal of this "second skin" is to manage the moisture and move it away from you without trapping your body's heat. The only time that cotton should become a part of your base layer is if you wish to keep cool, not warm, such as in a hot, desert climate where evaporative cooling becomes your friend, not your enemy.

To add to the base layer, you will want to have an arsenal of insulative layer choices and the goal here is a familiar one--provide warmth by creating dead-air space which slows the loss of body heat, as well as continuing to aid in the dissipation of moisture begun by your base layer. Since every person has different insulation requirements depending on body size, weight and fitness level, there is no pat formula for universal success. In general, I have found that the more options you have available, the more fine-tuning you can do and the more comfortable you will be on a daily basis.

For the initial layer or two I prefer pullover garments, but for that final just-in-case insulative layer, I opt for full-zip every time. You'll find that this allows the maximum versatility in ventilation management and makes this last layer much easier to put on and take off. I make sure that all my layers have roomy sleeves so I can push them up or slide them down. I also prefer zip-T necks as they ventilate superbly when open, yet insulate very well when zipped up around the neck. A chest pocket is a worthwhile feature too, as this provides a place to tuck a snack, a notebook, or some sunscreen.

Finally, you'll top the entire ensemble off with a thin windproof, water-resistant layer. You want this layer to breathe like crazy, yet not be so porous that rain runs through it like floodwaters through a leaking dike. I always look for jackets that are bright as well, since chances are you will be wearing them on dark and stormy days. I really appreciate the fact that a driver might see what he is hitting just before impact if I am at least making a loud visibility statement.

When selecting your shell jacket and pants, be sure that they offer enough room to accommodate layers underneath. The roomier the cut, the better the ventilation possibilities--no need to wear a garment that looks as if it could house the entire city of Los Angeles however. You don't want loose fabric that will flap around which goes double for the hood. For my active wear, I prefer a jacket with a thin hood that can be stowed into a zip-closed collar. When I'm running, blading or mountain biking, I rarely use a hood anyway and doubt if you will either unless the weather turns really ugly.

Ease-of-use cannot be stressed enough. If your layering system is a pain to take on and off, chances are you won't adjust the layers as frequently as you should and that defeats the purpose of layering all-together.

Why do I need all this fancy stuff just to go running, blading or biking? Fair question. Like the introduction of Gore-Tex years ago, all this fabric and fiber mumbo jumbo has its skeptics, but they are fast falling by the wayside. You don't have to opt for this aerobic function / fashion statement, but why on earth would you not want to? It works and it works leagues better than anything that has come before. With an appropriate layering system of advanced materials, weather is no longer a discomfort or nuisance--its just a pleasurable change of pace.