Beat Bugs: Thermacell Radius Zone Mosquito Repellent


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The sun was setting over a still, high-desert lake along the Pacific Crest Trail, 15 or so miles south of Timberline Lodge, Oregon. It was August 2018, I was well into my 24-hour birthday hike, and I wanted to enjoy the last rays and a snack before trekking on into the night. I sat down to take in the view of the lake, tents tucked between clumps of trees all around, but before I got comfortable a scourge of mosquitoes surrounded me. Disgruntled and without any defense against the vicious creatures, I got up and headed back down the trail, wishing I could just sit comfortably and enjoy the smells of the thick forest around me.

For nearly 20 years, Thermacell has been working to end the above scenario. In 2018, the Bedford, Massachusetts-based company debuted the Thermacell Radius Zone Mosquito Repellent, its first lithium-battery-powered device. This compact repellent relies on a rechargeable battery, unlike the butane-powered repellents before it, which means it can even be taken on airplanes. The active ingredient activates at a low temperature, so you don’t have to deal with a flame or liquid fuel. This also means there is no elevation ceiling, like other repellents on the market—so you can use it at sea level and high in the Colorado Rockies.

This spring, the company has made improvements, including a simplified user interface (tap one button for power, locking and the auto-off timer), a longer battery life and improved airflow, that offer better repellent distribution and more robust water and weather resistance.

Using it is simple. Just set it up, place it in the center of your campsite or rest spot and click a button to create a 110-square-feet mosquito-free zone. We found it so easy to use and small enough to take even on long backpacking routes. Tested by the Carroll-Loye Biological Research Laboratory in Davis, California, it’s made for anyone who wants to stop and smell the roses, pine trees or rich dirt without getting swarmed by mosquitoes.

Hands holding the Thermacell Radius, about to press the button.

It’s as easy to use as one touch of a button.

How It Works

A lithium-ion battery powers a heating element that activates the repellent at a low-level of heat, according to Thermacell. It continuously releases repellent to create an invisible protected area for up to six hours per charge. And it even works while charging, if you’re close to an outlet.

The active ingredient in the repellent, metofluthrin, is based on a naturally occurring repellent found in the chrysanthemum flower, which has historically been used to fight insects, according to Kyle Adelman, marketing manager for Thermacell. “Metofluthrin is in the pyrethroid family,” said Adelman. “Pyrethroids are synthetic replicas of the chrysanthemum. The reasoning behind using the synthetic version is it’s slightly altered on a molecular level and it performs better in this method of dispersion: heat. It’s more stable.”

Metofluthrin is also a pesticide and is regulated by the Environmental Protection Agency (EPA). That means it goes through rigorous third-party testing. “We use only EPA-approved repellents,” said Adam Chojnacki, vice president of product and innovation for Thermacell. “Development timelines are in years due to the complex level of research needed. We go through rounds and rounds of studies.”

That’s all before it heads to the Carroll-Loye Biological Research Laboratory to be tested for efficacy. There, according to Thermacell, scientists set up traps baited with CO2, which attracts mosquitoes, and a variety of repellents. They then release a specific number of mosquitoes, and, after a designated amount of time, they count the mosquitoes caught in each trap. They do tests with various amounts of time and distance, which is how Thermacell was able to make its time and distance claims (110 square feet and six hours).

Unlike products unregistered by the EPA, “all of our data and marketing claims have to be provable before we sell,” Adelman said. “It holds us accountable and honest. We literally can’t put a word on the package that the EPA hasn’t approved.”

When designing the Radius, Thermacell also aimed to cut down on waste. Previous Thermacell devices utilized both nonrecyclable fuel cartridges along with disposable repellent mats, which lasted up to four hours. The Radius only relies on a single repellent cartridge, which offers up to 40 hours of protection.

“In the realm of bug protection, this is the thing that people are talking about. It’s the only thing on the market like it,” said Dan Gilbert, assistant category manager for REI. He added: “It’s a pesticide deemed safe for humans in the amounts distributed by a Thermacell unit. Better yet, you are not having to put any products or scents on your skin.”

Two hands put the recyclable repellent cartridge into the device.

The device uses recyclable repellent cartridges.

How to Use It

While testing this product, we found it really easy to set up and use. Before heading out, charge the Radius through its USB port. It needs five hours to fully charge.

If you’re packing the Radius, slide the lock at the bottom of the device, and it won’t be able to turn on in your pack or luggage. If you’re on the move, “remove the repellent refill from the device and replace repellent refill cap,” per the instructions. The device meets TSA standards for approved air travel, but you’ll need to take the refill out of the Radius and place the cap on the refill before you take off.

Once you’re ready to use it, take the cap off the repellent cartridge, pop it in the device, toggle a lock and push one button. You’ll know it’s working because the light turns on. If you’re going to be using the device for a while, activate the timer, and it will turn off after a few hours.

Remember to read the instructions and follow all safety precautions. Also, metofluthrin should be kept out of bodies of water due to potential impacts to aquatic organisms. That goes for other similar products that use synthetic pyrethroids as active ingredients, as well.

Who Should Use It

We tried it out while camping, backpacking and resting during hikes, from densely wooded areas to high-desert locales around Washington state. We’ve even used it at a backyard party in Seattle. So if you’re adventuring into bug-infested areas, you’ll enjoy the Radius’ lightweight, portable design. It’s perfectly packable for hitting your local frontcountry or even international backcountry. It is less wasteful than other repellents and offers hours of protection, without the mess of spray repellents. As long as you’re stationary in the outdoors, it should work for you.

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