The camping glossary

Nobody is born knowing what a hydrostatic head rating is. The field assumes you do, which is exactly why buying a first camping kit feels harder than it should. If a term on this site is not in here, tell us and we will add it.

R-value

How well a sleeping pad stops the ground stealing your heat. Higher is warmer, and the numbers add up if you stack pads. Since 2020 every pad sold in the US is measured the same way under ASTM F3340, so brands are directly comparable. R 1-2 is summer, R 3-4 is three-season, R 5+ handles frozen ground. Full explanation.

ISO comfort and limit rating

The two temperatures a sleeping bag is rated at under ISO 23537. Comfort means a standardized cold sleeper is comfortable; limit means a standardized warm sleeper gets through the night curled up. The number in the bag's name is usually the limit, which is roughly 10 degrees colder than the comfort figure. Full explanation.

EN 13537

The older European sleeping bag standard, replaced by ISO 23537 in 2016. You will still see it on packaging. Both use a heated manikin on a standardized mat in a climate-controlled room, so the figures mean roughly the same thing.

Hydrostatic head

A tent fabric's waterproof rating in millimeters: the height of a water column the fabric holds back before water penetrates, measured under ISO 811. Family tents are usually 1,200-1,500 mm. Taped seams and full rainfly coverage matter more than the number. Full explanation.

Denier (68D, 70D, 600D)

The thickness of the yarn a fabric is woven from. Higher numbers mean thicker threads and generally more durability and weight. Useful for comparing two fabrics of the same type, useless as an absolute measure of quality.

Vestibule

Covered ground outside the inner tent, under the rainfly, where boots, packs and the cooler live out of the rain. The most underrated tent spec: a Kelty Wireless 6 publishes 19.5 square feet at each of two doors, which is more covered storage than a small backpacking tent's entire floor.

Footprint

A sheet of fabric under the tent that protects the floor from abrasion. It does not make a tent more waterproof, and if it sticks out past the floor it funnels rain underneath you. When it is worth it.

Rainfly

The waterproof outer sheet over a tent. A full-coverage fly reaches close to the ground and protects the walls and door; a partial fly covers only the top. Full coverage matters more than a higher fabric rating.

Freestanding

A tent that holds its shape without stakes, so you can pick it up and move it. Convenient on hard ground where stakes will not go in. It still needs staking down in any wind.

3-season

Spring, summer and fall: the rating on nearly every tent sold for camping. It means ventilation and rain protection rather than snow loading. Since almost everything is 3-season, the label rarely distinguishes anything.

Instant tent

A tent whose poles stay attached to the fabric, so it pitches in one to two minutes. You pay in weight and packed length: CORE's 9-person instant is 40 lb in a 48 in bag. The trade-off in full.

Packed weight vs trail weight

Packed weight is everything in the bag including stakes, guy lines and the bag itself. Trail weight is usually just tent, fly and poles. Compare like with like, and assume the higher number is what goes in your car.

Mummy bag

A tapered sleeping bag with a hood, cut close to the body. Warmer for its weight because there is less air to heat, and confining enough that some people sleep badly in one.

Quilt

A sleeping bag with the underside removed, since your body weight crushes that insulation flat anyway. Lighter, needs straps to seal it to your pad, and rarely carries an ISO rating. Bag vs quilt.

Fill power

How much space an ounce of down occupies, in cubic inches. Higher fill power means more warmth per ounce carried. 550-fill is a mid-range camping figure; 800-fill is premium ultralight territory.

Treated down (DriDown and similar)

Down treated to resist moisture, so it keeps some loft when damp and dries faster. It helps; it does not make down behave like synthetic. Wet down is still a cold night.

Self-inflating pad

An open-cell foam core inside an airtight shell. Open the valve and it draws air in on its own, then a few breaths firm it up. Warmest and most comfortable class of pad, and the bulkiest. Store it unrolled with the valve open.

Closed-cell foam pad

A solid foam mat that cannot puncture and cannot go flat. Thin and firm, typically R 2.0, and excellent as a second layer under an inflatable because R-values add.

Cot

A raised camp bed on a folding frame. Superb on rough or wet ground and easy to get out of, and cold in cool weather because air moves freely underneath. Put a pad on top below about 50 F.

BTU

British Thermal Units per hour: how fast a burner delivers heat. Watch whether a figure is per burner or a total. Coleman's Classic is 20,000 BTU total across two burners; Camp Chef's Everest 2X is 20,000 BTU per burner.

Propane vs butane vs isobutane

Three camping fuels. Propane works well below freezing and its 16.4 oz cylinders are sold everywhere in the US. Butane is compact and stops producing pressure near freezing. Isobutane blends split the difference and are the backpacking standard. The comparison.

Rotomolded cooler

A cooler formed in one piece with thick walls and a gasketed lid, so it insulates better and survives abuse. Also two to four times the price and much heavier empty: a YETI Tundra 45 is 24.6 lb before anything goes in it.

Ice ratio (2:1)

Two parts ice to one part contents, by volume, which is what a cooler needs to actually hold. YETI publishes this directly: 54 cans with no ice, 28 cans at 2:1. Every cooler behaves this way; most brands do not say so.

Block ice

A single frozen mass rather than cubes. Far less surface area per pound, so it melts more slowly. Frozen gallon water jugs do the same job and leave you with drinking water.

Lumens

Total light output. Peak lumens is a burst figure that most lights sustain for two to four hours; the low setting they can run for days is the number that matters. 100-200 lumens suits a tent, 300-600 lights a table.

IPX rating

Water protection. IPX4 is splash resistant from any direction, which covers rain. IPX7 is immersion to 1 m for 30 minutes. IPX8 is beyond that: Black Diamond specifies at least 1.1 m for 30 minutes on the Spot 400.

Watt-hour (Wh)

How much energy a battery stores, as against watts, which is how fast it can come out. A phone charge is roughly 15-20 Wh, so a 288 Wh power station is around a dozen charges. Nothing in that class runs a kettle. The math.

LiFePO4

A lithium battery chemistry used in newer power stations, rated for around 3,000 charge cycles to 80% capacity, several times the life of older lithium-ion. Heavier for the same capacity, and it lasts.

Guy line

A cord from the tent or fly to a stake in the ground, tensioning the structure against wind and keeping the fly off the inner tent. Skipping them is the usual reason a fly touches the inner wall and wicks water through.

Dark room technology

A coated tent fabric that blocks more daylight, so the tent stays dark after sunrise and somewhat cooler. Marketing name rather than a standard, and genuinely useful with children who wake at first light.

Greywater

Wash and rinse water from dishes. Scrape food into the trash first and dispose of the water where the campground directs, never into bushes or a stream.

Leave No Trace

The standard outdoor ethic: pack out everything you brought, camp on durable surfaces, dispose of waste properly, leave what you find, minimize campfire impact, respect wildlife and other visitors.