One of the coolest things about multi-day hiking is being able to arrive in a totally wild location, remove your backpack, and extract a shelter large enough to protect you and all your belongings from the elements. In other words: to carry your home on your back, like a highly-evolved snail. This housing miracle is more comfortable than ever today, due to the lightweight materials and advanced designs of modern tents, but the array of choice can be confusing. There are dozens of factors involved in tent design, and sometimes it's hard to know the differences between them. This simple anatomy lists the main features of a tent to give prospective purchasers a better idea of what to look for.
Shape: Tent shapes can be categorized into three main designs: tunnel, dome, and geodesic. Tunnel tents generally have more usable internal space and are very stable in high winds, as long as they are oriented correctly and securely pegged down. They usually have a single door with a vestibule (the covered area between the flysheet and inner door), used for pack storage and cooking in poor weather. Dome tents are freestanding, easy to move around and require only a single peg for each door (minimum), but lose out in stability. Two-person models have a door and vestibule on each side. Geodesic tents are similar to domes but have more pole crossings and are therefore more stable, and so are often used for mountaineering.
Inner Tent: The main body of the tent, the inner defines your living area and can be constructed of mesh (for warmer weather) or closed nylon (for cold). Climb inside to check dimensions, head height and usability. It should have multiple pockets, and a gear loft can be useful for extended stays.
Flysheet: Completely covering the inner, the fly is the protective shell of the tent, both waterproof and windproof. Most are made from nylon or polyester, the former being a stronger fabric but prone to sagging when wet. Ultralight models use DCF or Dyneema Composite Fabric, which is very light and very expensive. Flys are usually tape-sealed along the seams to prevent water ingress, and siliconized on the outside for extra strength. Some are siliconized on both sides and sewn with siliconized thread, removing the need for tape. The sun's UV rays are the biggest threat to flysheets; leave a tent up in the sun day-after-day and it'll degrade and tear much sooner than expected. Note the 'weight' or thickness of the fly material, measured in denier (D); 70D is relatively heavy; 7D is super light.
Single Skin: The reason tents have an inner and a flysheet, not just a single layer, is for breathability - such a design would drip with condensation during the night and soak the occupants from within. A waterproof/breathable membrane like Gore-Tex is not sufficiently breathable for a tent. A small number of high-altitude climbing tents do use this design for when temperatures are low enough to freeze the condensation, eliminating the problem.
Floor: As the layer that separates the sleeper from the ground, the tent floor is usually thicker and more abrasion-resistant than the walls. To save weight, some manufacturers keep the floor thin but produce a compatible groundsheet, or 'footprint', to protect it when necessary.
Hydrostatic Head: This is the measurement of how waterproof the materials are, and is measured in millimeters. It represents the height a column of water would have to be to push through the fabric. There is debate about how much is enough, or after which point it stops mattering, but a minimum decent figure would be 3000mm.
Pitching: There are three possible ways to pitch a tent: inner first (normal for dome and geodesic designs), outer first, or both together (normal for tunnel designs). The latter is called 'integral pitch' and is great for bad weather as it keeps the inner tent dry during the pitching process.
Poles: These are generally lightweight aluminum sections threaded together with bungee cord. The Korean brand DAC is universally regarded as the market leader. Remember not to 'snap' the poles out when pitching the tent. Although this might be tempting, it can severely weaken the ends and joints. Some tents are designed to be used with trekking poles, which is a good way of saving weight. Fiberglass poles are heavier and more breakable, and are no longer used in lightweight tents.
Pegs: There are various peg shapes on the market but Y- or V-shaped stakes are the best, and should be strong enough to withstand several blows from a rock without bending or breaking. Lightweight aluminum alloy or titanium are the best choice, and the tent should include enough pegs for all points and guy lines.
Guy lines: For extra stability in windy conditions, it pays to have at least four guy lines pegged out. They should have tensioning systems, and it's tidy if they have their own storage pockets.
Minimum Weight: This is a figure often quoted by tent manufacturers to make their tents sound lighter, and can be misleading. It can mean the weight of just the flysheet, poles, footprint and two pegs. The 'total weight' is a better representation of what actually needs to be carried on most hikes.