Best Backpacking Thermometer – Why You Need One and How To Choose

 The filter is a hollow membrane filter that is destroyed if it freezes.

The temperature was close to freezing but I didn't know if it was going to be 28 degrees that night or 38 degrees.

I couldn't risk losing my water filter so I had to sleep with it in my tent and hope the ambient temperature of my tent stayed above freezing.

That was the first time ever that I went backpacking and thought "Wow, I wish I had a thermometer right now".

If you don't want to read the whole article, here's a quick overview of the competition then my recommendation for someone looking to pick up their first backpacking thermometer. It's cheap, rugged and accurate.

If you're looking for the best of the best, you want a Kestrel.

I'll get into the differences between all of the models later, but the entry level Kestrel 2500 is my top choice for a premium backpacking thermometer.

If I had brought a thermometer with me to Colorado I would have been able to tell exactly what the temperature was. I could have been more prepared by protecting my filter from the cold or if it was warm enough, leaving it in my backpack and know that it wouldn't be damaged by freezing weather.

When most people hear about backpacking thermometers they usually dismiss them right away. But for less than $5 and under 1 ounce, you can pick up a quality thermometer that could give you peace of mind and heads up if your water filter is in danger of being damaged. A thermometer can also give you tons of useful info on what clothes you need to bring under different conditions.

Most backpacking water filtration systems use a hollow membrane filter. These filters have really small holes in them that block junk from getting into your clean water reservoir.

The problem with cold weather is that when water freezes, it expands. When you use your filter, even after the water has stopped flowing, the hollow membrane is still full of water. If this water freezes and expands it can permanently damage the membrane causing the 0.2 micron holes to become much larger which means all sorts of nasty stuff can get through into your clean water reservoir.

If you have a thermometer, you can monitor the air temperature and if it starts dropping to around 32 degrees Fahrenheit you can wrap your filter up in a bag and put it inside of your sleeping bag with you. Your body heat will keep the thermometer from freezing and ensure it isn't damaged.

If you do this, make sure the filter is wrapped up inside of a bag so water won't leak out into your sleeping bag. If you have a down sleeping bag and it gets wet, the down will clump up and won't keep you warm. Even if you have synthetic down, sleeping in a wet bag isn't fun so either way, keep your filter inside of a bag and keep it above freezing.

I know if it's above 60 and sunny then I'm comfortable in a t shirt and shorts. 

If it's going to be cooler than 40 degrees at night then I should wear at least shirts and pants to bed to keep myself comfortable during the night.

Having this kind of data on your own temperature preferences and knowing what clothing to wear in different conditions is extremely beneficial for planning what to bring with you.

Being an ultralight enthusaist doesn't mean cutting every last ounce without weighing the pros and cons. Having the (extremely small) additional weight of a thermometer could allow you to cut out unnecessary clothing on future trips and could end up saving you weight overall. If you know you're comfortable in shorts and a t shirt then you can leave the long sleeve shirt behind when the weather is above your cut off. But you won't know what your cut off is unless you take the thermometer with you and check actual temperatures while you're hiking.

Sleeping bags come with a temperature rating that is meant to tell you what temperature you'll be able to comfortably sleep in with a pair of patns and a shirt on while also using a sleeping pad.

You'll usually want to bring a sleeping bag that's rated for 10-15 degrees warmer than the temperatures you're expecting to encounter.  But some people "sleep cold" and others get hot no matter what. The temperature rating of a sleeping bag is a one size fits all approach and it might not match your needs.

By taking a thermometer along with you, you can track the temperature at night and see how well you slept. This will let you know if your bag is too warm or cold for the conditions you're expecting.  If a sleeping bag is rated for 30 degrees Fahrenheit and you get cold when its 40 degrees, then you'll know to bring layers with you next time. If your bag is rated for 40 degrees and you're sweating at night when it's 45, then you might want to switch to a 50 degree bag.

Bottom line is you need actual data to figure this out. You can't accurately guess what the temperature is; a thermometer is your only way to get a good measure on the temperature.

Backpacking thermometers range from simple traditional looking bulb thermometers that cost $5 all the way up to elaborate electronic devices that can measure wind speed, read humidity and capture data electronically to analyze when you get home.

In my search for the perfect backpacking thermometer I had a couple of features I used to compare the different options. 

Obviously the most important quality of a thermometer is that it can accurately read the temperature. If a thermometer can't do this basic task then I would never consider buying it.

Having a heavy backpack sucks. I want every piece of gear to be as lightweight as possible to make my hiking easier.

Smaller is better. I have a 60 liter pack but space is at a premium when I'm on longer trips. I don't want my thermometer to take up any more room than is absolutely necessary.

Durability for a thermometer comes in two parts.

The first is making sure it can hold up to the temperature and not just while hiking. If you fly with your backpack it can be exposed to very cold air in the luggage compartment of the airplane.

The second part of durability is the everyday wear and tear your gear goes through while backpacking. Stuff gets knocked around and crushed all the time when hiking so the thermometer shouldn't be fragile or prone to shattering.

The main use cases for my thermometer will be during the day when I'm hiking and at night when I'm sleeping. If you throw your thermometer in your backpack while hiking it will read a much higher temperature than what the actual air temperature is. Likewise at night, if you leave your thermometer on the ground it will be measuring the temperature of the ground which traps in heat during the day so it won't be accurate.

I want a thermometer that I can easily attach to my backpack and my sleeping bag to get accurate readings.

I didn't have any additional features I wanted in my backpacking thermometer but there are plenty of them out there. Some thermometers double as whistles or signaling mirrors for emergencies. Others have a compass built in or even a magnifying glass. 

A popular style of thermometer for backpacking is a digital one that records the min and max temperature. If you are looking for a min/max thermometer, here are some features you'll also want to look for:

• Recording min/max - This is handy because you don't have to constantly check your thermometer and monitor the temperature. You can just glance at it every 12-24 hours and see what the recent min and max temperatures were.
• Recording at least 24 hours - Some of the min/max thermometers only had a 24 hour memory. This can be a problem if your thermometer starts recording at 7 AM and you happen to wake up at 7:15 AM. If that data already got reset then you won't be able to tell what the overnight low temperature was.
• Long battery life  - The min/max thermometers are digital and rely on batteries for power. This is extra weight you have to carry and you don't want to worry about your thermometer running out of juice while you're hiking. You also don't want to carry extra batteries with you which is just more weight on top of the already heavy thermometer.

If you have a thermometer you use for cooking/grilling, you're probably wondering why you can't just bring that with you next time you go backpacking. Couple of reasons.

1. Kitchen thermometers are hard to read in direct sunlight. Backpacking thermometers are made to be used outdoors and are more durable and easier to read than kitchen thermometers.
2. The probe on kitchen thermometers is usually a long, sharp piece of metal so it can poke into a chicken breast or steak and read the temperature. This probe can be dangerous because of the sharp, pointy end. It's also much larger and bulkier than what you really need. This means extra weight and an increased risk that the probe can poke a hole in your backpack or sleeping bag. No good.
3. Kitchen thermometers are meant to be submerged in water or stuck into the food they're monitoring. They aren't as good at monitoring the ambient air temperature. Backpacking thermometers are usually more reliable and accurate.

There's a surprisingly large number of backpacking thermometers on the market. The first step for me was to narrow it down to a handful of choices that I could test and compare to find the best one. These are the 5 I went with.

Coghlan's basic thermometer checked all of the boxes for me. It's accurate, very cheap, durable, and can easily attach to my backpack or sleeping bag.

But as an entry level thermometer to have a rough idea of the temperature, Coghlan's thermometer gets the job done. It's also pretty durable but I wouldn't trust leaving it in the bottom of my pack. I just leave it attached to the outside of the pack in one of my exterior pouches and at night I clip it to my sleeping bag zipper.

Kestrel isn't a backpacking or hiking company. They specialize in handheld digital thermometers and wind meters. This means they're devices aren't small and they aren't as lightweight as some of the other options. But they are really accurate and pack a ton of features.

A backpacking thermometer might be one of the few gadgets that people think is unnecessary but ultralight backpackers will still bring it with them. From keeping your water filter safe to learning your comfort levels in different climates, a thermometer is an inexpensive piece of gear that could be a great addition to your pack.