Camping in 30 and 40 Degree Weather

Is 40 degrees too cold to camp?

No. Plenty of families camp happily in the 40s every October, and a clear night in the 30s is routine at higher elevations even in late summer. What separates a good cold night from a miserable one is almost never toughness. It is gear that was bought for July and clothes that got damp at dinner.

The number to respect is not the low on its own. The CDC points out that hypothermia can happen even above 40 degrees when someone is chilled by rain, sweat, or cold water. A dry 35 degree night is easier than a wet, windy 45 degree one. Plan for both the temperature and the moisture.

What changes as the low drops

• Low in the 50s. Most summer setups still work. A summer bag plus a fleece and a hat will usually get an adult through the night.
• Low in the 40s. Summer pads and air mattresses start to fail. This is where most first-timers sleep cold, usually from the ground up. A 30 to 40 degree bag and an insulated pad are the minimum.
• Low in the 30s. Dew turns to frost, water bottles left out can freeze at the top, butane stoves start to sputter, and tent condensation gets worse. You need a 20 degree bag, a pad of about R 4 or more, and a plan for keeping things dry.
• Low in the 20s. That is winter camping with different rules. If that is the forecast for a family trip, read winter camping for beginners and seriously consider a cabin.

Start with the ground, not the bag

The ground pulls heat out of your body much faster than the air does, and your weight crushes the insulation in the bottom of your sleeping bag flat. That is why people on an air mattress wake up cold with a perfectly good bag zipped to their chin. The air inside a plain air mattress cools to the temperature of the night and sits under you all night.

A sleeping pad's warmth is measured as an R-value. For nights near freezing, aim for a total of about R 4 or more. R-values add up, which makes the cheapest fix also the best one: put a closed-cell foam pad such as the Therm-a-Rest Z Lite Sol Foam Sleeping Pad (about R 2) under whatever inflatable pad or air mattress you already own. The foam cannot pop, and it works as a sit pad by the fire. If you do sleep on an air mattress, lay the foam pad or a thick wool blanket on top of it, between you and the cold air. The full explanation is in sleeping pad R-value explained.

Pick a bag rated below the forecast

Sleeping bag temperature ratings are more optimistic than most people expect. Bags tested to the ISO 23537 standard list a comfort rating (the temperature where a cold sleeper is still comfortable) and a lower limit (where a warm sleeper is comfortable curled up). Many budget bags only print one number, and it tends to sit nearer the lower limit. The lab test also assumes the sleeper is on an insulated pad and wearing a base layer.

A simple rule handles all of that: choose a bag rated about 10 degrees colder than the forecast low. For a 40 degree night, a 30 degree bag. For a night in the low 30s, a 20 degree bag such as the TETON Trailhead 20. If you sleep cold or want room to move, a roomy rectangular bag like the TETON Sports Celsius XXL 0°F Sleeping Bag gives you margin to spare. Already own a 40 degree bag? An insulated liner such as the Sea to Summit Reactor Extreme Sleeping Bag Liner is a cheaper upgrade than a new bag. Kids need the same margin; see the best camping sleeping bags for kids.

Not sure whether a mummy or a rectangular shape is right for your family? The trade-offs are in mummy vs rectangular sleeping bags.

What to wear to bed

• Change into dry clothes. The base layer you hiked in is holding sweat. Put on a dry set of synthetic or wool long underwear and dry socks right before bed, and keep that set only for sleeping.
• Wear a warm hat. It is the easiest piece of insulation to add and to take off at 3 a.m. if you get too warm.
• Skip the cotton. Cotton holds moisture against your skin and stops insulating once it is damp. Jeans and cotton hoodies are the most common cold-night mistake.
• Do not overdress. Piling on every layer can make you sweat inside the bag, and that moisture chills you later. Start with one dry base layer and a hat, and keep a puffy jacket within reach to drape over the bag if you need it.

The bedtime routine that keeps you warm

1. Eat something and have a warm drink. Your body makes the heat your bag holds in. A snack with some fat and protein before bed, and a mug of cocoa or soup, give it something to work with.
2. Take a bathroom trip right before bed. Getting out of a warm bag at 2 a.m. to walk to the bathhouse in the 30s costs far more warmth than the trip at 9:30.
3. Make a hot water bottle. Fill a sealed, hard-sided water bottle with hot (not boiling) water, check that the lid does not leak, wrap it in a sock, and put it in the footbox. For kids, an adult should fill and check it.
4. Keep your face out of the bag. Breathing into the bag adds moisture to the insulation. Cinch the hood around your face instead.
5. Keep tomorrow warm. Put the next day's base layer, your phone, and any batteries in the bag with you or in the footbox so they are warm in the morning. A few air-activated hand warmers make the first hour after sunrise much easier.

Kids lose heat faster than adults and often will not say they are cold. The kid-specific version of this routine, including what to do when a child wakes up cold, is in how to keep kids warm camping.

Pitch the tent somewhere warmer

Cold air is heavy and drains downhill at night, so the bottom of a valley or a low spot next to a creek can be noticeably colder than ground a little higher up. Pick a site slightly above the lowest ground, with some trees or a slope blocking the wind, and point the door away from the breeze. Choosing a site well is covered in how to choose a family campsite.

Then keep the vents open. It feels backwards, but a sealed tent on a cold night collects the water vapor from everyone's breath, and by morning the walls are dripping onto your bags. Damp bags insulate worse the next night. The fixes are in how to prevent tent condensation.

Never bring a fuel-burning heater, stove, lantern, or charcoal into a tent or a closed vestibule. They produce carbon monoxide, which you cannot see or smell. If you are tempted by a tent heater, read tent heater safety first, and for any night in a cabin or yurt with a heater, pack a battery carbon monoxide alarm.

The camp kitchen in the cold

Propane stoves keep working in the 30s, though the flame gets smaller as the canister chills. Butane stoves are the problem: regular butane stops turning into gas at about 31 degrees, so the slim tabletop stoves that work well in summer struggle on a frosty morning. The details and workarounds are in camp stove fuel in cold weather.

Plan one-pot hot meals rather than anything that needs a lot of standing around. Boil water once at breakfast and fill a vacuum bottle such as the THERMOS Stainless King Vacuum-Insulated Beverage Bottle, 40 oz, and you have hot drinks and instant soup all day without relighting the stove. Menu ideas are in cold-weather camping meals.

If you filter water from a stream or lake, protect the filter on nights near freezing. Sawyer advises tucking a used filter into a pocket or sleeping bag below about 33 degrees, and recommends replacing one you suspect has frozen, because ice can damage the filter fibers in ways you cannot see.

When to call it

A cold night is fine. A cold, wet night with wind is where trips go wrong. Head for a cabin, the car with the heater running in the open air, or home if:

• Rain or wet snow is forecast with lows near freezing and you do not have a dry place to retreat to.
• Sleeping bags or the only dry set of clothes got wet.
• Anyone shows the early signs of hypothermia the CDC lists: shivering, exhaustion, confusion, fumbling hands, memory loss, slurred speech, or drowsiness. Get them warm and dry right away, and get medical help if they do not improve.

Packing out early is not a failed trip. It is the reason the kids will want to go again. For handling a forecast that changes partway through a trip, see camping when the weather turns, and for the rest of the season's planning, start with fall camping for beginners.

Frequently asked

Is 40 degrees too cold to camp in a tent?

No. With a bag rated well below 40, an insulated pad, and dry clothes for bed, a 40 degree night is comfortable. Getting wet is the real danger, since hypothermia can happen above 40 degrees when someone is chilled by rain or sweat.

What sleeping bag do you need for 40 degree weather?

A bag rated about 10 degrees below the forecast low: a 30 degree bag for a 40 degree night and a 20 degree bag for the low 30s, used on an insulated pad.

What R-value sleeping pad do you need for 30 degree weather?

About R 4 or more in total. Stack a foam pad of about R 2 under an inflatable pad to get there, and never sleep directly on a plain air mattress on a cold night.

How do you stay warm in a tent at night in the 30s?

Insulate underneath, use a bag rated below the low, sleep in dry base layers and a hat, eat before bed, use the bathroom right before you lie down, and put a sealed hot water bottle in the footbox. Never use a fuel-burning heater inside the tent.