Science of Clothing

There is more to dressing appropriately for an outing than wearing the latest fashions on the trail. 

Science of Keeping Warm

Your body produces are certain amount of heat dependent on your activity level.   A person at rest produces a certain amount of heat.  A person running produces more heat.

The temperature outside can increase or decrease your body temperature.  In the Pacific Northwest, it generally cools your body. 

Exposure to direct sunlight can heat up your body.

Exposure to water and rain will cool your body.  In fact, rain and wetness can easily lead to hypothermia if you can't or don't protect yourself.  Wetness is generally the biggest concern when it comes to selecting clothing.

The idea of insulation and clothing is to keep your body temperature in a safe and ideally comfortable range.  Not too hot and not too cold.  Do so by carefully selecting the proper mix of clothing based on your level of activity and environment.

Heat Loss Through Head

You DO NOT lose half of your body heat through your head.

Myth: "You lose 40 to 45 percent of body heat through your head"

Origin: US Army Survival Manual: FM 21-76: US Department of the Army, 1970:148

Context - based on 1950's research where soldiers were dressed up in arctic survival suits, minus headgear. Most of heat loss was through unprotected skin - their head since the rest of their body was well insulated from the cold.

Debunked: Vreeman RC, Carroll AE. Festive medical myths. BMJ. 2008;337:a2769. Published 2008 Dec 17.

Black Clothing

Article in January 1980 Nature reports that the amount of heat gained by a Bedouin exposed to the hot desert is the same whether he wears a black or a white robe.

What does this have to do with hiking?  Not sure, but it's a fun article.

Ref:  Shkolnik, A., Taylor, C., Finch, V. et al. Why do Bedouins wear black robes in hot deserts?. Nature 283, 373–375 (1980).

Methods of Heat Transfer

Conduction

• Transfer of heat through direct contact

• Water conducts heat about 25 times that of air

  • Getting wet is the biggest concern for hypothermia

  • It is import to avoid getting and staying wet from rain, immersion in lake of from sweating

• Metal is even a better conductor of heat

  • Contact with subfreezing metal can cause flash frostbite

Convection

As you heat the air around your body, the warmed air tends to move upwards and is replaced with colder air.  As the wind blows, heated air around your body is blown away and replaced with colder air.

Evaporation

Water on your skin is heated by your body.  This water is composed of a mix of water molecules bouncing around at different speeds.  Higher energy molecules in the water escape via evaporation, leaving lower energy molecules behind.  This leads to a cooling effect as the average temperature of the water on your skin drops.  Your body heats up the water on your skin and the cycle continues until all water has evaporated.

Radiation

Heat radiate from your body and other surfaces via infrared radiation.  This mostly happens at temperatures below 20°C (~70°F).

Respiration

As you breath in cold air, it is heated up and moisturized in your lungs.  With each breath, you lose body heat and water.

Layering

The purpose of layering is to protect you from the cold, while allowing you the ability to select layers needed for your particular environmental conditions and activity level.

Base Layer

Wicks water away from your body, limiting heat loss through evaporation and conduction.  Also provides various amounts of insulation.

• Under Armour style wicking layer

• Cycling pants

• Polyester or similar synthetic thermal layer

• Wool thermal underwear

• Military ECWCS Base layers

Mid Layer

Insulation layer.  Limits heat loss, generally through trapped air pockets within insulation material.

• Pullover (sweater)

  • Polyester, wool or fleece

• Fleece Jacket

• Puffy Jacket

Outer Shell

Protect inner layers from rain and wind.

• Ideally Waterproof Breathable

  • Special material such as Gore-Tex or comparable

  • Seam taped or welded

• Windproof Softshell

  • In area where rain is NOT an issue (Dessert)

  • Breathes better than waterproof shell

• Water Resistant Shell

  • Where only very light rain is possible or likely

  • More economical than Waterproof Breathable

• Vapor Barrier Jacket

  • Where downpours happen sporadically and you can dry off afterwards

Laying allows you choose which layers are needed for a particular activity dependent on weather.  Can be easily adjusted as needed.

Fabric Material

Cotton

Cotton is a popular fabric for workwear since it is comfortable, breathes, is durable and is easy to wash.  It is NOT ideal for hiking and other outdoor sports where you can get rained on, will sweat a lot or otherwise get wet without being able to go indoors and dry out.

Cotton insulates by trapping air within its fibers.  Thick cotton sweatshirts can feel very warm when dry.  The problems with cotton is that it can absorb up to 27 times its own weight in water and keeps that water next to your skin.

Water conducts heat and leads to evaporation.  When cotton gets wet, it loses its ability to insulate.  The water trapped in the fabric drastically increases heat loss via conduction and evaporation and takes a long time to dry out.  Wet cotton clothing can lead to hypothermia.  This is were the saying "Cotton Kills" comes from.

Canvas can be treated with Durable Water-Repellent Coatings (DWR), but it is still far from being ideal for outdoor events in the Pacific Northwest. 

Cotton should be avoided, except in very hot environments where hypothermia is not a concern.

Synthetics

Nylon, Polyester, Polypropylene and similar products are hydrophobic.  They don't absorb very much water and dry quickly.  If they get wet, they can be wrung out or shaken and your body heat will generally dry them out quickly.  These are the preferred fabrics for outdoors activities in wet or cold environments like the Pacific Northwest.

• Polypropylene

  • Absorbs almost no water

  • Great insulator

  • Horrific stink associated with this fabric is why it isn't the primary fabric used for outdoor clothing

• Nylon (aka polyamide in Europe)

  • Stronger and stretchier than polyester

  • More silky feel than polyester (but some polyesters are catching up)

  • Dries quickly

• Polyester

  • Absorbs less water than nylon

  • Better abrasion resistance than nylon

  • "Warmer" than nylon

  • Dries quickly

Wool

Made up of very fine animal hair.

• Wool

  • Sheep, goat, rabbit hair

• Fleece (animal type)

  • Llama or alpacas hair

  • often just called wool to avoid confusion with polyester fleece

• Merino wool

  • Merino sheep hair

  • Found in mountainous regions of Australia and New Zealand

• Cashmere wool

  • Cashmere goat hair

  • Fine, soft, downy, winter undercoat

• Qiviut wool

  • Musk oxen hair

Wool is hygroscopic (absorbs moisture from air).  Since water molecules are trapped in the fibers of wool, it tends to feel dry when damp (up to 30% of weight).  It maintains its loft (trapping air pockets) to a certain degree when it gets wet, therefor allowing for some insulation when wet.  Wet wool is warmer than wet fleece.  Wet wool takes longer to dry out than wet fleece.  Wool breathes better than fleece.

Merino wool supposedly generates heat when water is absorbed within its fibers.  This occurs from a chemical reaction.

• weatherwool.com/pages/the-science-of-wool

• www.woolwise.com/wp-content/uploads/2017/05/03.2-The-Wool-Fibre-and-its-applications-Notes.pdf

Wool seems to keep you cool when hot. It is preferred by many over synthetics in moist (not pouring rain) environments where it can absorb some water while still feeling dry. 

Wool is more expensive and heavier than other synthetic fabrics.

Fleece

Most fleece is made from 100% polyester.  Some or mixed with other fabrics such as spandex (to make stretchy) or even cotton.

The fabric is often brushed to make it fluffy.  This gives it a soft feeling and traps air for insulation.  It was designed to mimic wool.

Fleece is moisture wicking and hydrophobic.  This pulls water to the surface of the fabric where it can evaporate away from your skin.  Fleece doesn't get water logged like cotton o down.  It wicks moisture better than wool and dries quickly.

Many companies use the Polartec Scale for measuring the thickness of Fleece (100, 200, 300).  100 weight fleece weighs 100 grams per square meter of fabric.  Heavier weight fleece is thicker and warmer.

Air and water passes through polyester fleece easily.  This keeps you relatively warm and dry.  Thicker fleece doesn't breath as well as thinner fleece.  Sherpa fleece (heavyweight and fluffy) doesn't breath as well as micro fleece.

Fleece is preferred over wool if you are going to get really wet.

Examples:

• Lightweight

  • REI Co-op Groundbreaker 2.0 ($50)

  • Patagonia R1 TechFace Hoody ($189)

  • Outdoor Research Vigor Full Zip ($110)

• Midweight

  • Arc'teryx Covert Cardigan ($180)

  • Patagonia Lightweight Synchilla ($129)

  • Patagonia R1 TechFace Hoody ($189)

• Heavyweight

  • The North Face Denali 2 ($179)

  • Military Polartec fleece

Puffy Jacket

Consists of a inner and outer fabric layer with loft material trapped between these layers.  The shell may not breath as well as fleece or wool, especially if it has a heavy duty waterproof or windproof outer layer.

Down Puffy Jacket

• Made from feathers.  Loft determined by type/quality of feathers.

• Very compressible

• Lightest weight material for insulation

• Expensive

• Mats when wet and loses ALL insulation value

• Slow to dry

• NOT recommended for younger scouts or in wet environments

• Can get stinky - especially low grade down

• Examples:

  •  Patagonia Down Sweater ($279)

    • 3.0 oz. of 800-fill-power down

  • Mountain Hardwear Ghost Whisperer/2 Hoody ($350)

    • 3.0 oz. of 800-fill-power down

  • REI Co-op 650 Down Jacket 2.0 ($100)

    • 4.2 oz. of 650-fill-power down

Synthetic Puffy Jacket

• Doesn't insulate as well as down (weight per insulation value)

• Insinuates when wet

• Dries quickly

• Doesn't compress as well as down

• Heavier than down

  • Weight can vary a lot depending on how jacket is built

• Far less expensive than down

• Examples:

  • Arc’teryx Atom LT Hoody ($259)

  • Patagonia Nano-Air Hoody ($299)

  • Cotopaxi Teca Cálido Hooded Jacket ($150)

  • Military field jacket liner

Soft Shell

Generally designed to be windproof and water resistant.  They breath better than waterproof shells, but not as well as fleece.  If you are using a hard shell jacket, you should not use a windproof inner layer.  This reduces overall breathability and doesn't provide as much insulation as midlayer fabrics per weight.

Examples:

• Arc’teryx Gamma LT Hoody ($249)

• Black Diamond Dawn Patrol ($200)

• Outdoor Research Ferrosi Hoody ($129)

Water Resistant Shell (aka Rain Shells)

Fabric may be shed some water as opposed to sealing out water.  Generally NOT seam sealed.  Generally a less expensive option where a completely waterproof layer is overkill. 

Multipurpose windproof layer.

Examples:

• Nylon treated with DWR (Durable Water Repellent)

  • Carhartt Shoreline Jacket

• Tightly woven or treated Polyester

Waterproof Breathable Shell

Made with special vapor permeable fabric such as Gore-Tex, eVent or other similar product.  Water vapor passes through membrane so you don't get as wet on the inside while shedding water on the outside.

This layer is a must in western Washington, Oregon and British Columbia.

"Hardshell" vs "Rain Jacket"

• Hardshell

  • 3-Layer construction

    • Usually thicker outer layer - treated with waterproofing agent

    • Middle breathable membrane layer

    • Inner layer protects membrane and feels soft

  • More durable and heavier that "Rain Jacket"

  • Examples:

    • Arc’teryx Beta AR ($599)

      • Gore-Tex Pro

    • Outdoor Research Microgravity ($249)

      • AscentShell

• "Rain Jacket"

  • 2 or 2.5 layer construction

  • 2-Layer

    • NO liner (membrane comes in direct contact with your skin)

      • May use mesh to separate skin from membrane

    • Generally not very breathable

    • Generally more affordable

    • Examples:

      • Columbia Watertight II ($60)

        • Omni-Tech

      • REI Co-op Groundbreaker 2.0 ($70)

        • 2-layer waterproof breathable laminate

      • Montbell Versalite($219)

        • 2L Infinium

  • 2.5-Layer

    • very thin interior fabric printed on waterproof/breathable laminate or coating

    • Made to be lighter in weight

    • Usually less expensive than Hardshell

    • Inner layer is slippery or plasticky compared to 3-layer fabrics

    • Pack better than 3-layer jackets

    • Examples:

      • REI Co-op Rainier ($100)

        • 2.5L Peak

      • Black Diamond StormLine ($159)

        • 2.5L BD.dry

      • Outdoor Research Helium Rain ($159)

        • 2.5L Pertex

      • Patagonia Calcite ($299)

        • Gore-Tex’s Paclite Plus

Waterproof Vapor Barrier Shell

Plastic or rubberized outer layer blocks all water.  Great for economical layer in areas with occasional down pours.  Wearing it will trap water vapors on the inside and make you feel wet and muggy.

Not a great option for long hikes or outings.  These have been replaced with breathable fabrics that won't leave you soaking wet with sweat.

Examples:

• Frog Toggs

  • Polypropylene with Dripore Gen 2

  • Said to be breathable - but not enough to keep you dry if when moving

  • Very economical option

• Polyethylene

  • Carhartt Lightweight Waterproof Rainstorm Coat

  • Emergency/disposable ponchos and raincoat

  • Degradable PE poncho and Degradable PE raincoat

    • Biodegradable

  • Trash bags

• • • Contractor grade trash bags have many uses - cut a hole in the bottom and it turns into a poncho

• PVC (polyvinyl chloride)

  • Fisherman jackets

• EVA (Ethylene-vinyl acetate)

  • more stretchy and softer than PVC material in cold weather

  • more eco friendly than PVC?

• PU (Polyurethane)

  • Better for cold/wet weather - Scandinavia area

  • Used as workwear

  • Pleather

    • aka leatherette, imitation leather, faux leather, vegan leather, PU leather

    • Pleather can also be polyester treated with imitation leather finish made with polyvinyl chloride (PVC), or polyurethane

• Rubberized Coats

  • "Mac" (named after Charles Macintosh)

  • Army Poncho is ripstop nylon with a polyurethane coat

• Waxed or Oiled Fabric

  • Comfort and style of cotton with some protection from rain

  • OK of camping - not ideal for hiking

  • Waxes:

    • Carnauba wax

      • Brazilian palm tree

    • Paraffin

      • Petroleum product

    • Microcrystalline wax

      • Petroleum product

      • Generally darker, tackier, and more heat resistant)