Thermacell MR300 Insect Repeller Review

© Dan Bailey

Do you ever get sick of wearing insect repellent, or blundering around half-blind inside a head net? I certainly do. Wouldn't it be nice if someone could invent a gadget that stopped biting insects getting near you in the first place? Thermacell devices are new to the UK, and we were offered one to test back in the height of summer. It sounded promising, but of course not all insects are created equal. Thermacell might work on mosquitos - reports from the States are certainly encouraging - but how does it fare on Scottish midges? I've been trying to work that out for a few months. And...? Well I'm still not sure. Yes, sometimes, maybe...

One of the 'portable' range, the device is light-ish and reasonably compact  © Dan Bailey
One of the 'portable' range, the device is light-ish and reasonably compact
© Dan Bailey

What is it and how does it work?

Thermacell devices create an insect repellent zone that's said to deter small flying insects. The several different models in the range all operate on the same principle: A small butane cartridge acts as a portable heat source; this heat is directed to a metal grill, which holds a replaceable mat saturated with repellent; the substance is thus dispersed into the air... and (hopefully) off the mozzies buzz.

To get it started you simply turn a dial and press an ignition switch. The heat is safely contained in the unit so you can pick it up and place it on different surfaces while it's operating. And the resultant vapour cloud is more or less odourless.

We were sent the MR150 to review: it turns out that only the MR300 is available in the shops here, but the difference between the two is merely cosmetic.

Each mat lasts up to 4 hours  © Dan Bailey
Each mat lasts up to 4 hours
© Dan Bailey

What's the active ingredient?

The stuff that does the business is allethrin. I asked Wikipedia for help:

The allethrins are a group of related synthetic compounds used in insecticides. They are synthetic pyrethroids, a chemical found naturally in the chrysanthemum flower. They are commonly used in ultra-low volume sprays for outdoor mosquito control including many household insecticides as well as mosquito coils.

Apparently the compounds have low toxicity for humans and birds, but you certainly don't want to get too close. And keep cats away, as allethrins are toxic to them.

What's the effective range?

Thermacell claim that their devices provide a 15-foot safe zone - I guess that's 15 feet in all directions. Of course we've not been able to verify the range precisely, but it does seem sufficient to cover a camping spot and would probably work for a belayer too. When camping in a group, for instance, we've used one device for the common area between tents. It takes a few minutes to come into full effect. It only needs a bit of breeze, however, and that chemical zone is bound to disperse. If there's enough wind to affect the Thermacell then it'll probably be enough to keep the midges grounded - the problem being that when the wind drops again the midges are back straight away, while it takes some time for the Thermacell to re-establish its protective zone. This device is only ever going to work to the best of its ability on dead still evenings - the times you'd most need it, basically.

Its protection zone should be large enough for a valley basecamp  © Dan Bailey
Its protection zone should be large enough for a valley basecamp
© Dan Bailey

Has it been tested on the highland midge (culicoides impunctatus)?

Short answer: no. This is an American device that's been developed with other bugs in mind.

"We have had a few reviews but none in the highlands" the UK distributor tells me. "Thermacell is new to the UK, however it's been selling in America for years and the reviews are very positive."

Having read the reviews on Thermacell's own website I'd say the reactions are strikingly polarised. It either seems to work perfectly, in which case it's the best thing since sliced bread, or people say it has no impact at all. The positive reactions are in the majority.

But while mosquitos are very unpleasant, and in some parts of the world keeping them away is literally a matter of life or death, any UK user is going to know full well that, when it comes to sheer annoyance and persistence, not all small biting insects are equal. The midge, particularly the voracious Scottish variety, is infamous for laughing at repellent and for swarming in thousands.

So does it actually work on midges?

I have to admit I've been dreading writing this review, because that question seems to be both fundamental, and to defy a neat yes/no answer. Midges are too small and fleeting to count, and they wax and wane with every breath of wind; so how, in an outdoor environment, might a normal person like me devise a fair test for any repellent? I can only offer anecdotal evidence.

Summer evening in Glen Brittle - nothing short of a flame thrower is really going to dent the onslaught  © Dan Bailey
Summer evening in Glen Brittle - nothing short of a flame thrower is really going to dent the onslaught
© Dan Bailey

When the midges are swarming like a biblical plague I think it's fair to say that nothing yet invented is going to reduce the madness to bearable levels, short of giving up and going indoors. Repel five in ten and you'll still have a hundred up each nostril and thousands in your hair. On just such a midsummer evening on Skye - hot, windless and midge infested - we tried to gain some respite with the Thermacell MR150. After about half an hour of hopping around wearing headnets it still hadn't thinned out the hordes so you'd notice. Even holding the device up at head level seemed to make no difference - but then how could it? So far, so inconclusive.

Some weeks later on a still and humid camp in Borrowdale, the rather tamer Lakeland midges were just enough to be a biting nuisance. I stuck the device on the table, and around 15 minutes later we realised that although the odd midge could still be seen, no one was being much bothered any longer. I'm pretty sure the wind was the same, and that the only material change had been turning on the Thermacell. I chalked that one up as a success.

On several other camping evenings, where midges were also present in low numbers, the Thermacell did seem to make some sort of difference too; but again it's very hard to say how much. Not once have I been bitten by a mosquito while using the Thermacell - I have however received hundreds of midge bites in the line of duty. It's clearly not a silver bullet.

I'd say that for moderately midgey conditions it's probably better than nothing, but that when midge-mageddon strikes the Thermacell is as effective as anything else - which is to say, not very.

What does a long-term user say?

I've only used this unit for a few months, but I know a man who's had one for seven years, so I thought he'd be worth asking:

"My experience has been that if used exactly as recommended - i.e. allow about 10-15 mins burn time for it to warm up, keep it completely flat and use it when there is little wind - it is pretty effective in creating a safe space within a limited sheltered area - enough for a tent entrance or for a couple of people sitting cooking" says Colin Wells.

"It seems to shoo away most insects - including non-target species. I have observed foraging beetles for example changing direction abruptly and high-tailing it out of the exclusion zone at a rate of knots."

"However, I think you are correct to assume it has its limits and that mass midge attacks may well overwhelm it. So far maybe I have just been lucky. What I would say however, is that if there is intermittent breeze it loses effectiveness completely. Often such conditions would also deter midges from flying, but in peak conditions when there are gusty breezes and then lulls, it can give an opportunity for the vampiric blighters to continue business as usual."

"So I've never relied on it completely and always have a Plan B. In the end, nothing really beats Smidge, if you want a midge/cleg/mozzie bite free day."

"My answer to the question: 'Does it work?' is: 'Sometimes, depends...'"

Thanks Colin!

Not for use in confined spaces, like a closed tent  © Dan Bailey
Not for use in confined spaces, like a closed tent
© Dan Bailey

Are there any health recommendations or use restrictions?

The idea of sitting in a chemical cloud doesn't really appeal, but weigh this against the possibility that you might not also have to wear insect repellent - itself often quite nasty stuff.

This advice is from the company's website:

Only for outdoor use as an insect repellent. Do not use indoors, in tents or in any enclosed area. Do not insert anything other than Thermacell mats into the appliance. Cover or remove all exposed food. Do not leave appliance unattended or use in windy conditions. Do not expose appliance or mats to rain. Do not attach appliance to your body or clothing. Place appliance on a flat, stable surface with the grill facing upward...

The advice on confined spaces would have been good to know before I used it all evening in a zipped-up tent awning (there's nothing like reading up on a product before pressing the switch). I won't do that again. But it has to be said that my tent was virtually midge-free while the air just outside was thick and humming with them - so in close quarters the Thermacell clearly works, even if that's not recommended for your health.


The MR150 weighs about 180g, plus a bit for the gas cartridge. It's a robust device, but quite bulky, and between the size and weight I'd be unlikely to pack it for my usual weight-conscious backpacking trips. For me this is more of a car camping thing.


All Thermacell devices take the same butane cartridges and repellent mats. A standard refill pack costing £7.99 buys you three replacement mats, each lasting up to four hours, and one gas cartridge with a 12-hour burn time. I reckon the running cost to be about £1.50 per hour, which if you can feel it working is going to be money well spent.


I'm sorry not to offer a definitive answer to the all-important midge question. In my experience Thermacell has certainly seemed effective in low midge densities, but it's snookered if there's an intermittent breeze. In a full-on swarm any protection it can offer is simply overwhelmed. At £30, plus the running cost, it's not wildly expensive. It may not be dramatically better than a topical insect repellent, but neither is it noticeably worse, since none of them work as well as you'd hope anyway. In that sense it's a string that may be worth adding to your bow if you regularly camp in the British summer. However, do not expect miracles. I won't be dispensing with my Smidge and head net just yet, but at least now I have a third option too.

Thermacell say:

The Thermacell MR300 Portable Mosquito Repeller effectively repels mosquitoes by creating a 15-foot protection zone. The MR300 Repeller can be taken virtually anywhere outdoors to repel pesky mosquitoes, stopping them before they can bite or bother you. The MR300 is the newest Thermacell portable mosquito repeller, boasting some new and improved features.

  • Quiet ignition, Reengineered grill and switch, Improved ergonomics, and Accessory mounting system
  • Ideal for repelling mosquitoes from the backyard to the great outdoors
  • Portable and lightweight
  • No spray and no mess
  • Scent-free and DEET-free
  • No open flame, no smoky candles
  • Package contains: 1 Olive MR300 Repeller and 12 hours of refills - 3 repellent mats and 1 fuel cartridge
  • MR300 £29.99
  • Halo Mini £34.99
  • Backpacker £44.99
  • Scout Lantern £56.99
  • Bristol Lantern £34.99
  • Standard refill pack £7.99

For more info on the MR300 see

Thermacell MR300 prod shot

25 Sep, 2018

 I can't believe he has left the car door open in that second picture!

Must have taken a few days to get them all out. Little bastards.


25 Sep, 2018

I've used the Thermacell for around 4 or 5 years now in Finland. Works really well, on damp & sheltered crag bases to protect the belayer from mossies and small amounts of midges. Don't have sandflies here, so can't say. Neither can I recall if they help with horseflies. So they are quite nice for projecting sessions (be it boulder or roped stuff), in generally protected forests (ie. no wind). And naturally for say flyfishers (and hunters in a shooting booth), the latter being the ones I recall it was originally designed for (hunters & fishers).

25 Sep, 2018

I’d just like to thank Dan for volunteering to be the crash test dummy. 

26 Sep, 2018

"At £30, plus the running cost, it's not wildly expensive."

I see it's essentially the same insecticide as a mosquito coil.

£30 plus proprietary refills is a lot more expensive than a mosquito coil holder at about 6 quid.  The added bonus of the ones that sandwich the coil between glass fibre nets is that you can burn it at both ends.  Or break it in half and burn it at 4 ends, or more if times are desperate.  The coils are cheap, leave no waste apart from a little ash, and come with no plastic packaging.  Also it's immediately obvious when they've run out - is that the case with the Thermocell refill thingy?

27 Sep, 2018

The wee bastards are impervious to anything short of these:

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