What is the Difference Between Base Layer Apparel and Regular Thermal Underwear?

Believe it or not, we tend to get a lot of questions about underwear.  One of the questions people ask is: what is the difference between "baselayer apparel" and "thermal underwear?"  A corollary question to that is: "what is the difference between the various fabrics used to make base layer clothing and underwear today?"

Most standard undergarments today are made from cotton or poly-cotton fabrics. These traditional materials can retain perspiration and so can be uncomfortable.  This dampness means that standard underwear carries the risk of chilling the wearer during colder temperatures. To combat this and provide better flexibility in a variety of environments, a variety of performance fabrics and fabric thicknesses are used to provide an insulating layer between the wearer's skin and his or her outer apparel, helping wick away moisture while maintaining a comfortable body temperature. In most cases, next-to-skin apparel is classified by type of fabric and fabric weight. Depending on your specific needs, different combinations are often recommended for different circumstances.

Who uses base layer apparel?

Base layer apparel is often worn by military personnel because they are often subjected to extreme cold weather environments.  U.S. military personnel in the Air Force, Army, Marines and U.S.C.G. / Coast Guard often wear multiples levels or baselayers as part of their ECW clothing systems.   Runners and other athletes, outdoor enthusiasts, and many types of workers, such as commercial fishermen and sailors, also often wear baselayer apparel.

Why would you need base layer apparel as opposed to standard underwear?

Base layer apparel is typically meant to be worn to limit discomfort due to moisture from perspiration, which normal undergarments can cause, as well as to help regulate body temperature depending on the environment. In colder environments, heavier base layer clothing is recommended, and typically is designed a snug fit and elastic cuffs to keep body heat inside the garment. Lightweight base layer garments are designed to be loose to promote air circulation while wicking moisture away from the skin, increasing overall comfort and reducing the risk of heatstroke.

What types of fabric are used in base layer apparel?

Most base layer underwear is made from one of three types of materials: silk, merino wool, synthetics such as polyester, or high performance flame resistant materials.

Advantages of Base layer shirts and pants made of Silk fabric:

  • Recommended for cool-weather temperature ranges and lower activity levels
  • May be treated to enhance moisture wicking properties
  • Transports moisture more slowly than synthetic fabrics
  • Has a luxuriously comfortable texture
  • Layers excellently and adds little to no bulk
  • Disadvantages include poor abrasion and UV resistance and the need for frequent laundering to avoid odor buildup

Advantages ofBase layer pants and shirts made of Merino wool:

  • Recommended for colder temperature ranges, but good for most conditions
  • Excellent insulating properties
  • Naturally antibacterial and thus has significantly less odor retention
  • Moisture evaporation keeps skin cool and reduces overheating due to warmer temperatures or extreme exertions
  • Merino wool is preferable as a wool fabric due to its softness and relative comfort compared to other types of wool
  • Disadvantages include expense of garment compared to synthetics or silks, and reduced drying rate when wet

Advantages of Base layer tops and bottoms made of Synthetics:

  • Best for high-humidity or warm conditions, but usable for all activities and climates
  • Includes rayon, nylon, polypropylene, polyester, spandex, and other synthetic blends
  • Resists wrinkling and abrasion
  • Soft, comfortable texture when worn
  • Easily laundered
  • Disadvantages include vulnerability to staining and odor retention if worn repeatedly over multiple days

Advantages of traditional thermal underwear tops and bottoms made of cotton and poly/cotton blends:

  • Comfortable
  • Inexpensive
  • Easily laundered
  • Often called "long johns," they are usually made up of a long sleeve shirt and long pants or drawers

What types of fabric weight are used in base layer apparel?

Most manufacturers of thermal undergarments and moisture-wicking underclothing use four general titles for fabric weights.

  • Ultralightweight: Sometimes referred to as silkweight or microweight, these are intended for use in mild to cool conditions, and are primarily intended for moisture wicking with minimal heat retention.
  • Lightweight; Intended for use in cool to moderately cold conditions where thermal protection is not required but adds to overall comfort.
  • Midweight: Intended for use in moderately cold to cold conditions where thermal protection is required, and commonly worn as part of a clothing layering system.
  • Heavyweight: Intended for use in extremes of wind and cold weather in which thermal protection is necessary as part of a clothing layering system, with some manufacturers using 'expedition weight' to indicate even heavier fabrics.

There are a number of brands manufacturing quality baselayer apparel today. Some of the leading brands include United Join Forces, Drifire, Massif, Indera Mills, Tru-Spec, Helly Hansen Workwear and Under Armour.