This is the foundation of the layering system. Its job is to be comfortable and wick moisture away from the skin to regulate temperature when you are static or in a high-intensity activity. The most common base layer types are Merino wool and polyester. Each has its pros and cons. Merino Wool: is a natural fiber that keeps you warm when wet, naturally anti-microbial (for multiday trips or hunting), and has a higher insulation ratio. Typically, wool products are more expensive than polyester. Polyester: is a man-made fiber that dries faster, lightweight, but tends to hold odor even with applied anti-odor treatments. Also, it stays cool when wet, which is not always optimal in cold conditions.
Level 2 will be your fleece layer [think textured grid fleece or a more traditional polar fleece] or heavyweight base layer over 230g/m2. These garments can be made from synthetic fibers like polyester or nylon or natural fibers like wool or cashmere. This is an important layer because it continues to move moisture away from L1 and your skin but is substantial enough to keep your body heat trapped when static. These items are typically close-fitting pull-overs or zip-up mock neck tops and jogger-type bottoms. This layer can be worn alone or combined with a tighter-fitting base layer depending on conditions and user preferences.
When selecting these garments, you will have lots to choose from. Many companies make these in all types of silhouettes, weights, and fills. The selection of this highly depends on the end-use and environmental conditions of the activity. For the most warmth in a cold and dry environment, nothing compares to the insulation of a 900-fill power goose down outerwear. Think of this layer like the fiberglass insulation in a house that keeps out the cold and traps in the heat during winter. Down gives you the most warmth by trapping air in between soft, puffy plumage clusters. Humid or wet environments require synthetic insulations made from polyester fibers either as a blown fill that goes into baffles or sheeted materials to be cut & sewn directly to the fabric. Most of these jackets have a down-proof treated synthetic shell to protect the insulation and to eliminate wind penetration. These fabrics will also be treated with a DWR [durable water repellent] finish to keep off light rain or mist.
  
Softshell garments are a versatile layer that can be used as both outerwear or the fourth layer in a 5-layer system. The purpose of this layer is to keep out wind and light rain in order to retain the body heat you are holding inside the other mid and base layers. Windbreakers fall into this category because we are looking at a garment that isn’t necessarily seam-sealed like hardshell outerwear meant for rainfall. Bonded soft shells combine multiple layers of an abrasion-resistant face fabric which is bonded to an interior fleece or mesh knit backer. This allows the user another option of wearing the soft shell either as a replacement layer for an insulator or midweight base layer when needing to reduce bulk or weight in more favorable weather conditions.
  
L5/ Hard Shell
Like the shingles on your home’s roof, this essential layer keeps out tempestuous wind and torrential rain. Quality technical outerwear should allow you to be in heavy rain and yet still remain dry. But to stay comfortable it also should allow your sweat to evaporate as your activity level increases. The key is to properly maintain the cleanliness and DWR of the garment throughout its lifecycle. The hard shell typically has an extremely durable face fabric finished with a DWR [durable water repellent] treatment to make the rain bead up and roll off the face fabric. This prevents water from pooling together, saturating the face fabric, and leaking into the interior. A waterproof membrane keeps the rain droplets from penetrating the microporous openings but allows the moisture vapor particles produced from your body to escape. A lightweight interior backer fabric keeps the membrane protected from potential oil and dirt contamination from the wearer’s skin. If you are going to invest any of these layers, we suggest you do it with your outerwear. Look for water-tight zippers, like YKK AquaGuard® and fully taped seams to ensure that the garment takes every step to seal out water penetration. Other key features include pack-friendly pocket positioning, fully adjustable hoods, and other draw-cord adjustments to help seal out wind and snow. And for extreme stop & start end-use activity, convenient venting options located under the arms or thighs to quickly cool down the body’s core are just as important.
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