Beyond Clothing
A working field guide to everything but the clothing: hydration, sun, physiology, what danger looks like, and how to manage the shifts, rooms, and nights you can't opt out of.
This is the reference we wish we had when we started testing gear in the desert: the set of things that have kept us comfortable, and occasionally kept us safe, across dry canyons, humid coasts, and the cities in between. Clothing recommendations appear where they belong, in context, and we name other companies' products freely, because pretending to be the whole answer would not help you.
In this guide
- Hydration: how much, what to drink, what to watch for
- Sun protection: sunscreen, eyewear, what fabric does and does not replace
- Heat physiology and acclimatization
- When heat becomes dangerous
- Working when you can't stop
- Cooling a room you can't air-condition
- Sleeping through heat
The numbers, before you go
1 to 1.5 liters per hour
What active hot-weather exertion can demand. Pre-hydrate; the body cannot replace what it does not have.
Electrolytes after 2 hours
Water alone dilutes blood sodium toward hyponatremia. Add electrolytes for anything sustained.
Thirst is lagging
By the time you feel it, you are already down enough to dull thinking and pace. Drink small and often.
Hydration
The advice to drink eight glasses a day was never written for someone working in extreme heat. Active hot-weather exertion can require 1 to 1.5 liters per hour, sometimes more. The body cannot replace what it does not have, so pre-hydrating before a long day matters as much as drinking during it.
Water alone is not enough over long durations. Sweat carries sodium, potassium, and other electrolytes out with it. Replacing only water dilutes blood sodium and can produce hyponatremia, which mimics dehydration but is worse and more dangerous. For sustained effort beyond two hours in heat, add electrolytes. Liquid I.V., LMNT, and Nuun all do the job; so does eating something salty at a rest stop.
Thirst lags behind need. In dry heat, by the time you feel thirsty you are often already 1 to 2% dehydrated, enough to measurably dull both thinking and physical capacity. The habit that works is small amounts, often, with urine color as your gauge.
In humid heat the picture shifts. Because sweat evaporates poorly, the body sweats more to compensate, and total fluid loss can exceed a dry day even at a lower temperature. The feedback is misleading: dry heat feels dry, humid heat looks drenched. The dry scenario is the more dangerous of the two, because the loss is hidden.
Reading the color
A rough gauge, not a diagnosis. Pale straw is the target and deep amber means drink now. Color also shifts with food, vitamins, and medication, so read it alongside timing: many hours with no need to go is its own signal.
Sun protection
Sunscreen and UPF clothing do different jobs. Sunscreen protects exposed skin; clothing protects covered skin. Neither replaces the other.
For exposed skin, mineral sunscreens built on zinc oxide or titanium dioxide sit on the surface and reflect UV. They work on contact and stay stable over time. Chemical sunscreens absorb UV through reactions that consume the active ingredient, take 15 to 20 minutes to bind, and degrade with exposure. For multi-hour days in the sun, mineral formulas are generally the more reliable choice. Reapply every two hours, more often when sweating heavily or swimming.
The ratings matter less than people think above a point. SPF 30 blocks about 97% of UVB; SPF 50 blocks about 98%. Above SPF 50 the added protection is small. The higher number buys a little more time before reapplication.
Eyewear is underrated. UV exposure to the eyes accumulates and contributes to cataracts and macular degeneration. Sunglasses rated UV400 or 100% UV are the standard, and wraparound styles are worth it in deserts where UV reflects off pale sand, rock, and salt. Lips are the most forgotten surface of all: lip skin has no melanin and burns fast, so an SPF balm belongs in every kit.
Heat physiology and acclimatization
The body adapts to heat over 7 to 14 days. The process raises your sweat rate, lowers the sodium concentration of that sweat, increases plasma volume, and lowers your heart rate at a given workload. Someone two weeks into a hot climate tolerates it far better than someone who flew in yesterday.
If you are flying from a temperate place into a hot one, plan for the first two or three days to be limited and save the hardest hikes for later in the week. Acclimatization also decays on a similar timeline once you return to cooler weather, so someone who lives in San Diego and visits Big Bend each July re-acclimatizes every trip. A gentle hike on day one prepares you better than shade does.
When heat becomes dangerous
Two heat illnesses are worth knowing by sight. They sit on a continuum, and the first becomes the second if it is ignored.
Heat exhaustion
Looks like: heavy sweating, weakness, fatigue, dizziness, nausea, headache, cool and clammy skin, fast pulse, body temperature normal or slightly raised (below 104°F / 40°C).
Do: stop, move to shade or a cooler space, remove excess clothing, drink water with electrolytes, and rest. Recovery is usually quick with the right response.
Heat stroke · medical emergency
Looks like: body temperature above 104°F / 40°C, hot skin that may be dry or still sweating, confusion or altered mental state, rapid pulse, possible loss of consciousness or seizures.
Do: call 911, move to shade, and cool aggressively by any means available, cold-water immersion if possible, wet cloths to the neck, armpits, and groin, and fanning. Do not wait. Heat stroke can cause organ failure and death within hours.
The signal that matters most is mental state. A hiker who is dizzy and hot but lucid is in exhaustion territory. A hiker who is confused, slurring, or acting strangely is in stroke territory and needs immediate cooling and care. When in doubt, treat it as the more serious version. Watch your partners for the early signs, irritability, clumsiness, reduced urination, headache, and remember that prevention through water, electrolytes, pacing, and a willingness to turn around is worth far more than any rescue.
“The wisest people we know in heat read the day correctly and choose to come back to it.”
Working when you can't stop
Everything above rests on a freedom a working day removes. A hiker sets the pace and turns back; a roofer, a farmworker, a warehouse picker, a line cook cannot, and heat that would end a hike is a shift someone still has to finish. The strategy shifts from choosing your exposure to controlling the few things still in reach.
The most dangerous stretch is the first few days, and the acclimatization timeline above is the reason. The workplace record is stark: a large share of on-the-job heat deaths fall in a worker's first days, and they disproportionately strike the new hire and the person back from a two-week vacation, including people who handled the same heat fine last season. The rule that prevents them is a ramp: start a new or returning worker near a fifth of the workload and build to full over about a week. Skipping the ramp is the most common way the worst days happen.
The number that outranks the thermometer.
Air temperature undersells the danger because it ignores humidity, sun, and exertion. The measure that predicts collapse is wet-bulb globe temperature, and the practical hinge sits near 82°F WBGT: past it, heavy continuous work needs enforced work-rest cycles, and by the upper 80s even light work does. That is often a plain-air reading in the mid-90s°F with sun and humidity. The free OSHA-NIOSH Heat Safety Tool computes it from your phone's location. When it says slow down, slow down.
Past the first week the discipline is the work-rest cycle, and the ratio shifts further than instinct suggests: as heat and effort climb, more of every hour has to become rest in shade.
Moderate heat, moderate effort
Work ~45 min. Rest in shade ~15 min.
High heat, or heavy effort
Work ~30 min. Rest in shade ~30 min.
Extreme heat and heavy effort
Work ~15 min. Rest in shade ~45 min.
The split is directional; real ratios depend on the actual heat load and workload, and the tool above gives specifics. What holds everywhere is the direction: hotter and harder means more rest, which is the reverse of how a crew under deadline behaves. Rest also only counts if it cools you: shade, moving air, water, and in dry conditions a wetted shirt.
The hydration chapter above covers the basics; a long shift adds two cues. Electrolytes matter more at hour eight than at hour one, because plain water across a long, sweat-heavy day is what tips into hyponatremia, so the salt belongs late in the shift as much as early. And when urine color is unreadable, on a night shift or buried in gear, track timing instead: many hours with no need to urinate is a dehydration signal even absent thirst.
Clothing helps where the work allows it, light, loose, and breathable, but much protective gear traps heat and removes that lever entirely. Where the gear is fixed, the load shifts onto rest, water, and shade, because those are what remain. The mental-state rule above applies double on a crew: the person sliding toward heat illness is the last to know, and on a job the call to stop is often not that worker's to make. That is why it has to be a crew habit and a supervisor's duty, set before the hot day arrives.
Cooling a room you can't air-condition
A building is a heat battery. Sun drives energy through the glass, the structure stores it, and by evening the walls radiate that load back at you for hours after the outside air has cooled. Cooling a space without a machine means blocking heat by day and dumping it by night, and the moves that do this are mostly the opposite of what feels right in the moment.
Open windows help only when the air outside is cooler than the air inside. On a hot afternoon that condition is false, so open windows import heat. The rhythm inverts: seal the windows and shades through the day to keep the cooler air you banked overnight, then open everything once the outdoor temperature drops below the indoor temperature, usually late evening to just after dawn, and flush the stored heat.
Point the fan out
Cross-ventilation does the flushing, and its direction matters. Set a box fan in a window on the downwind, shaded side blowing out. Exhausting hot air creates suction that pulls cooler night air through windows opened on the opposite side, and it moves far more air than a fan pointed inward, which only stirs the air near itself. One fan blowing out plus a distant window cracked open beats two fans blowing in.
Stop sunlight outside the glass
The biggest lever is stopping sunlight before it becomes heat, and it has to happen outside the glass. Once light crosses a window the energy is already in the room; an interior blind then only chooses where it lands and re-radiates. Exterior shades, awnings, or a shutter on the sun-facing side cut the load by roughly half compared with interior curtains, which is a larger effect than most air conditioners contribute. A pale or reflective exterior surface beats a dark one. Where only interior shading is possible, close pale, reflective-backed blinds before the sun reaches the window, not after it is already streaming in.
Use thermal mass
Thermal mass is a lever most people never touch. Dense surfaces, tile, concrete, stone, plaster, stored coolness the same way they store heat. Running the night flush across a masonry floor or a tiled room pre-loads it with cold that bleeds back into the space through the next afternoon; a heavily carpeted, all-drywall room has almost nothing to hold that charge and heats up faster. It is also why basements stay cool: earth-coupled mass barely moves in temperature. When you can choose where to spend the worst hours, spend them low and on hard floors.
When a fan stops helping
A fan cools skin rather than air, by speeding evaporation and carrying warm air off your body, and that only works while your skin is warmer than the air. Once the air passes the mid-90s°F, hotter than skin, a fan blowing on you convects heat into your body and speeds dehydration. In extreme heat, pointing a fan at yourself is worse than still air. The fix is to keep using the fan to exhaust a room while keeping it off your body, and to wet your skin first so there is water for the moving air to evaporate.
Kill the heat sources inside
Kill the heat sources you are feeding the room with. An oven or stovetop, a running dryer, incandescent bulbs, and a gaming PC each dump real wattage into the space; a single old bulb wastes most of its energy as heat, and an oven can raise a small kitchen several degrees. Cook cold, cook outside, or cook at night, and switch off what is idling. One counterintuitive move for dry climates only: a wet sheet hung in the airflow, or a shallow pan of water in front of the exhaust fan, adds evaporative cooling as the water changes phase. In humid air it does the reverse, loading an already-saturated room with moisture and making it clammier: it helps in a dry desert and backfires on a humid coast.
Sleeping through heat
Falling asleep requires your core temperature to drop about one degree, and it sheds that heat into the room and bedding around you. A warm bedroom blocks the drop, which is the physiological reason a hot night means lying awake at 2 a.m. rather than merely feeling uncomfortable. Cool the room first with the flushing rhythm above, and keep the bedroom sealed and shaded all day so it is not radiating stored heat at bedtime. Then work the few inches that actually touch you, which outrank the room temperature here.
What touches your skin
Fiber against skin decides how well heat leaves you all night. Natural, hydrophilic fibers, linen, cotton, hemp, pull moisture off the skin and pass it on; synthetic sheets and sleepwear trap heat and hold sweat against you, which is the exact clammy signature of a bad hot night. Looser and lighter wins over more of it. A hydrophilic fiber behaves against skin at night the same way it does on a trail, and a still, hot bedroom is the plainest demonstration of the difference we know.
Three tricks that sound wrong
A warm shower an hour before bed cools you: warming the skin dilates surface vessels, and in cooler air afterward the body sheds core heat faster than if you had done nothing. Damp socks, or a bare foot out from under the sheet, punch above their weight: the feet carry dense networks of vessels built to dump heat, so cooling them cools all of you. And a water bottle filled and left in the freezer becomes a reusable cold pack for the bed, best placed at the ankles or behind the knees where blood runs close to the surface.
The last details
A cool, damp cloth on the wrists and neck at lights-out helps, water by the bed replaces what you sweat before it wakes you, and a fan set for a light draft across the bed carries heat off your skin, within the limit the callout above describes. If only one room can be made sleepable, make it the lowest and least sun-exposed one and move the bed there for the worst nights; sleeping arrangements are easier to change than building physics.
Most of what this page asks for is small: a liter carried, a window sealed at the right hour, a break taken in real shade, salt late in a long shift. The margins add up quietly, and in a bad heat week they are what you will be living on.