The harness is the essential piece of equipment for any mountaineer who wants to tackle a via ferrata.
There are two types of harness: the sit harness, made up of a waist belt and leg loops, and the chest harness. The chest harness used in combination with the sit harness makes up what is called a full-body harness.
The sit harness consists of a fairly wide waist belt. Depending on the brand and the model it can be more or less padded, so as to be more comfortable for the wearer and, naturally, to soften the jolts in the event of a “whipper” or a “fall”. On the sides the harness has gear loops on which you can clip karabiners and any other climbing gear. Above all, remember that these loops are in no way meant to secure the mountaineer: you cannot and must not rely on them in any way for the mountaineer's safety. Besides the waist belt, the sit harness has two leg loops, that is two more or less padded rings you put your legs through. The leg loops are joined to the belt at the front by a solid tape belay loop, and at the back by a strip of tape (sometimes elastic) whose only job is to stop the leg loops from twisting about.
The sit harness is particularly comfortable for sport climbing or in all those winter mountain situations in which it would otherwise be awkward to wear a full-body harness, which would hardly go well with the padded or heavy clothing needed at high altitude. Another advantage of the sit harness is how quickly you can put it on or take it off.
The full-body harness can be useful if you want to feel safer and more protected, or for particularly inexperienced or clumsy hikers who are tackling a via ferrata for the first time. The full-body harness also stops the hiker from flipping over backwards in a fall with a heavy rucksack.
A sit harness can be combined with a sling of tape tied around the shoulders and arms, so as to make a full-body harness quickly and simply. The tape is tied into a loop and worn so that it forms an X across the back; the two ends of the loop are then joined at the front with a karabiner, which in turn connects the sit harness to this “improvised chest harness”.
In mountaineering in general it is better to use a harness than an improvised tie-in made of a simple rope knotted around the waist. The harness is a safer piece of mountaineering equipment, tested when it is manufactured and easy to use. For those who are not great experts in mountaineering knots, wearing a good harness means avoiding being accidentally hanged, strangled or just tangled up in a badly used rope.