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Bill – The reason varying thicknesses and types of base layers are manufactured is that for being active in a specific effective temperature range, just the base layer and a wind shirt provide thermal comfort while eliminating the hassle factor of adding and removing the insulation layers.
For example, I frequently hike the Northern CA coast during the summer. The day time temperature range is 45 to 75F, the wind is 0 to 35 mph, and the sky is foggy to clear. These changes can occur in short order as fog and wind belts are encountered and then blocked along the coast.
If I follow conventional wisdom and select my lightest base layer, it would be my Patagonia Capilene silk weight crew. I need to augment it with a mid weight fleece insulation layer or my Patagonia Micro Puff vest and a warm hat. During the course of a day I end up taking the insulating layer and warm hat in and out of my pack many times. With a thickness for temperature range optimized base layer hoody, I never need to stop and open my pack to put an insulating garment on or off… I just zipper adjust or flip a hood while on the move.
A COOL/COLD weather temperature range optimized base layer has two purposes: 1) keep your skin dry; and 2) provide the variable insulation required for the combination of your MET rate and the effective environmental temperature. For purpose 1) It needs to fit tight to effectively wick moisture away from the skin. This is the reason Power Dry and Power Stretch are engineered to be very stretchy. Merino wool garments use a knit pattern to also be stretchy. Non stretch and non bi-component fabrics, such as Polartec 100, will wick moisture away from your skin 30% less effectively than Power Stretch or Power Dry. Capilene will wick well only if worn skin tight.
For purpose 2) they need to effectively evaporate water off the outside of the insulation. The bi-component nature of Power Dry and Power Stretch are designed to accomplish this. The internal buffering moisture storage of Merino wool also accomplishes this in a different fashion.
A wind shirt, in combination with the hoody base layer’s ventilation options, provides a very wide range of insulation values without having to add or remove an insulating hat or insulating mid layer garment the majority of the time. In addition, a hooded wind shirt that is sealed up provides up to .8 clo by preventing the air layer around the body from being blown away. A hoody’s base layer garment ventilation options include: stretchy sleeves that can be pushed up or down, deep neck ventilation zippers, tight fitting hoods that can be quickly flipped up or down, and thumb holes that can be quickly slipped into or out of. These integral adjustment options allow the base layer’s effective insulation value to be varied over a very wide effective temperature range without having to stop and get into the pack to add or remove garments.
Edited by richard295 on 08/29/2007 12:47:37 MDT.
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