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Feedback on Base Layer


I noticed an article in this months Trail Magazine on base layers.  They featured an Xcelcius Megatherm top that claims to be certified down to -25c.  I have had a look on their website and it looks to be good but can't find any reviews on here so don't know if it is a new brand.

Has anyone on here used this garment before and have any feedback or advice.

I am planning a trips later in the year to Snowdonia and trekking in Scotland when it will be very cold so this could be ideal.

Any advice would be great.

Many Thanks,


Most people here on Trailspace are in the US. I note that Xcelsius is UK, and that you give the min temp in °C (equivalent to -13°F), suggesting that you are in the UK as well.

I am always a bit skeptical of temperature ratings for clothing, even when the claim on the website is that it is "certified". Although the CE rating system is more or less standardized, it does leave some "wiggle room", since individuals differ greatly in their comfort zone, as well as from day to day, depending of factors like fatigue, how recently they have eaten, etc. Another factor is that the top you cite is only one layer - you won't generally be wearing it as your only clothing. The outer layers come into play as well.

Having said all that, and having no experience with the brand, as you stated, it looks to be worth looking at, trying out, and writing a review here, albeit a little pricey at close to £30

That is interesting, BillS. How does one shirt like that even GET a rating down to minus 13 degrees. Having lived in a climate with winters that go sub zero, I don't think there is a shirt on the planet that is good to go into cold weather on its own.

i  think temperature rating depends on a lot of factors.  i can think of situations where i wore a baselayer on its own in sub-zero conditions; i was hiking up a mountain carrying a large backpack, and i wasn't exposed to high wind. 

on the other hand, i haven't used any base layer that i could even think about wearing alone in sub-zero weather while standing still. 

Well there is always this option(not sure if it can be recharged with a Goal Zero though...)

I do think that the -25c is a stretch though from being out in temps that cold but then again with the way technology is anymore my mind is open to the possibility. 

When it sounds too good to be true... or sounds just plain ludicrous.

yeah, but where do you put the battery...up your wazzoo? it is lithium ion so the cold shouldn't affect it as much but still...

Is it just coolmax and polyester or something new?

I would layer two thin merino tops, a long sleeve underneath a larger sized t-shirt (a la Tipi Walter). EDZ is good value in the UK; Wiggle has some bike ones that are almost as good, often on sale.

Beware of the magazines and their sustainers: if the weather paid for adverts it would always be sunny.

Certified by whom?  The base layer will not make the difference in cold weather.  It is part of the clothing system.

I regard this is a "part of this complete breakfast" type claim!

Certainly any base layer can be part of a clothing system that might be effective within a certain range of temperatures,  but to make a specific claim and assert that it is broadly applicable is pretty dubious.

Thanks for your feedback guys, I am indeed in the UK.  Looking at their website they actually ship internationally so wasn't sure if they had a customer base or reputation in the US.

I was a bit sceptical about the certified claim myself but to be fair to them they don't make claims that you can wear this on its own in sub zero temperatures.

I asked them for more information and the feedback i received was that their megatherm garments were tested against a standard ISO 9920 which is "Ergonomics of the thermal environment - Estimation of the thermal insulation and evaporative resistance of a clothing ensemble".  So they pretty much confirmed that it is part of a layered system.

I decided to take a punt (an english expression) and ordered a set which were delivered yesterday.  Although not being able to test in a minus 25C environment it is currently sub zero temps her in the UK I have tested out the top.  It is extremely thick, although I expected this considering its specs and wore it out to take my dog for a walk this morning with no other layers.  I can report that it was very effective, comfortable but very warm.  I just wish I had worn gloves!

All in all am initially impressed with the product and i am confident it will be fine for my trip later in the year.

Mumbo jumbo.

haha, thanks for the constructive comments ppine. just providing feedback.  seems to me that combined with the right system this probably does "what they say on the tin".  The standard looks legit from what I have read on the internet.  can't comment until used in colder temperatures though.

Interesting! My google search led to pages like, which sells gear for workers in extreme conditions. Which means I might find it in Newfoundland's fishing/oilrig outfitters. It's also recommended by the UK's SAR people.

Apparently it's made of polyester blended with "Viloft", which is made from wood pulp. Wood pulp! There's none of that in my closet right now. I'd really like to know how this performs. I suspect it would do very well wicking sweat and managing odour. Wood is naturally antibacterial. This gear is not very expensive, either. And, possibly, enviro-points for the renewable resource.

Also interesting: "Ideal for off shore fishing, petro-chemical rigs, railways, construction, highways, for for outdoor sports such as skiing, snowboarding and mountaineering. Ideal for frozen food production." Well, sign me up! I believe ice fishing counts as frozen food production, doesn't it?

Please report back when you've had some more experience with it, Paul. Is it itchy? Does it dry quickly? Does it keep its shape? Thanks very much!

Postscript: The 'Vi' in 'Viloft' twigged me (sorry) to go check Wikipedia. Yes, some viscose fabric (rayon) is made from wood cellulose. Perhaps this is like a thick plush version of rayon? That would be nice and comfy...

Wouldn't you want to keep it away from petroleum products aka OIL RIGS lest you burst aflambe?

Hi Islandness, looks like you have done a bit of research.  I can confirm the Viloft elements of them.  I have only worn it so far in the mornings for short periods of time but haven't experienced any itching at all.  Very soft and comfortable actually.  Hasn't lost any shape either.

My Cabela's Power Dry Polar Weight gridded fleece underwear (zip T-neck) keeps me very warm for the weight. I use it for cold days when ski patrolling under a sweater and love it.

The gridded inside creates warm air spaces and gets rid of sweat quickly. This stuff is amazing, even warmer and drier than my older Cabela's Thermastat poly fleece longies.

I think some of you have misread the ad and description of the shirt. Turnip is right, the maker does not claim it will keep you warm at -25C. The ad says it is "certified" for use down to -25C, which is entirely different. What that means is a bit unclear, but it seems to mean the fabric will not absorb moisture and freeze up in extreme cold. In other words, it works like Capilene or similar synthetic fabrics in extreme temperatures. The ISO standard is ISO:9920-EN340 which applies to clothing, but I haven't seen an actual rating like that for a sleeping bag under EN 13537 for this shirt, but I assume there is a similar testing procedure. The standard mentions "ensemble" so any rating would be based on an ad hoc collection placed on a mannequin.

Found this description of the standard on a website

ISO 9920:2007 specifies methods for estimating the thermal characteristics (resistance to dry heat loss and evaporative heat loss) in steady-state conditions for a clothing ensemble based on values for known garments, ensembles and textiles. It examines the influence of body movement and air penetration on the thermal insulation and water vapour resistance. It does not deal with other effects of clothing, such as adsorption of water, buffering or tactile comfort, take into account the influence of rain and snow on the thermal characteristics, consider special protective clothing (water-cooled suits, ventilated suits, heated clothing), or deal with the separate insulation on different parts of the body and discomfort due to the asymmetry of a clothing ensemble.

I have a Capilene Expedition Weight top and I bet this is somewhat similar. By comparison, my top lists for $100 US, so 25-30 or so pounds is not overly pricey.

I read Wood pulp! And the wise guy just has to come out in me...

So do you need to worry about termites?

It was just the other day i was reading about the water proof wind proof new fabrics that are not either,  until they have been properly 'teased'!

No one here even wants to know what I have been saying to my closet.

IMO it won't work..... I am allergic to polypro's and it makes me itch. Wool does not.

I use duofold longies a 2 layer fabric cotton inside wool outside. With a wool dress shirt and a down vest i can do -13F easy so long as i am moving/working.

I doubt i would be happy in a single layer though.

turnip said it was thick. I imagine it would have to be. I think it's too good to be true.

September 21, 2020
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