Buying a harness can be a daunting task, especially for the new rock climber. There are a wide variety of harnesses on the market and a lot of lingo and jargon to sift through. The first stage in the selection process is deciding the intended use. The second stage involves dialing-in fit and features.
New buyers will find an explanation of basic components and features a good jumping off point.
Buckles: There are two types of buckles: manual double-back and auto double-back. Manual double-back is more adjustable. It is also easier to put on over multiple layers of clothing, mountaineering boots, crampons, and skis. Auto-double back usually adjusts more quickly and snugly, with less room for user error; however it can be cumbersome to get on over mountaineering equipment.
Waistbelt and Leg Loops: These are the parts of the harness that correspond with their respective body parts. Some have padding to add comfort while some have none at all. These components are usually fastened or adjusted with buckles. On sport harnesses the leg loops are often fixed without buckles.
Gear Loops: Gear loops are the part of the harness on the waistbelt used to clip carabiners and all sorts of other equipment. They act as the pockets of the harness. While they can carry a lot of gear, THEY ARE NOT LOAD-BEARING.
Belay Loop: The belay loop is the strongest point on the harness where locking carabiners are connected for belay devices and rappelling. It should not be used as a single tie-in point.
Haul Loop: This is a small loop on the back of the waistbelt which is used for trailing a second line or haul line. Some are load bearing and others are not.
Tie-in Points (Hard Points): These are the two loops (one on the waistband and one connecting the leg loops) where the climber ties the rope to the harness. They are also connected by the belay Loop on most harnesses.
Four Categories of Harnesses: There are four main categories of harnesses on the market Sport/Gym, Trad/Big Wall, Ice/Mixed, and Alpine/Mountaineering. While these categories are useful in retail shops and online marketing materials, most harnesses will work for many climbing applications.
Sport/Gym: Sport/Gym harnesses are lightweight and more minimalist, as the goal is usually to climb hard and press limits. These harnesses generally have fewer gear loops, smaller belay loops, no haul loops, and less padding in the waist and legs. Often the leg loops are not adjustable and the waist band has an automatic double-back. Harnesses with no padding and only one tie-in point are generally to be avoided.
Traditional/Big Wall: Traditional (trad) harnesses usually have a few more features to help with comfort and gear management on longer climbs. These are often good all-around harnesses that will work for trad, gym, sport and even some ice and mixed climbing if leg loops are adjustable. The sacrifice here is a little more weight for additional functionality.
A typical trad harness will have more padding in the waist and legs. This helps a lot when hanging in the harness for long periods of time. A good trad harness should have at least four gear loops. Most will have adjustable leg loops. The buckles could be either manual double-back or automatic double-back. Many trad harnesses will also have a haul loop on the back of the harness.
Big wall harnesses are essentially the next step up from a trad harness. They commonly have the most padding, as big walling involves hanging in the harness for extended periods of time. They usually have the most gear loops, as well, and some even have two belay loops to help manage aid climbing gear.
Ice/Mixed: Ice and mixed climbing harnesses are very similar to trad harnesses, with some minor differences for climbing in cold, wet, snowy environments. They usually have adjustable leg loops to accommodate for multiple layers of clothing. Additionally, the material is often treated to help minimize the absorption of water. Some ice/mixed harnesses have a bit less padding as they assume the user will be wearing some extra clothing to help with the padding. They generally have at least four gear loops. Some even have specialized gear loops for ice screws. Ice and mixed harnesses may or may not have haul loops.
Alpine/Mountaineering: Alpine and mountaineering harnesses are the most minimalist of climbing harnesses. They are generally lightweight with no padding, and worn over many layers of clothing. They are also used used in climbing conditions where a fall is unlikely, such as snow climbing, glacier travel, and ski mountaineering. These harnesses generally have at least a few gear loops. Some do not have belay loops. An important feature of these harnesses is their ability to go on easily and quickly over large boots, crampons, and even skis. For this reason the leg loops are usually fully adjustable, as is the waist belt. While these harnesses are generally the cheapest, they are not recommended for general rock climbing due to their lack of features and comfort.