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Best Trekking Baselayer Bottoms

The F-Lite Megalight 140 Base Layer Half Shorts - A Year-Round, True Baselayer

F-Lite's Megalight 140 Base Layer 1/2 Shorts


The F-Lite baselayer bottoms are a year-round baselayer. In winter we pair these with the Odlo Cubic Tights (now called "Active F-Dry Light Leggings") which are also reviewed here. This combination has been tested in a windchill ("feels like temperature") in the minus 20s °C. Also, in this review we mention an additional layering option which double as a spare / emergency / civilised, clean, return journey pair. These can be used to layer over the Cubic's if temperatures drop into the extreme sub zero temperatures. However, the final conclusion and rating are solely related to the F-Lite 140s.

Please note the materials stated below are correct, yet most sites including F-Lite's own, state they are a Polyamide, Polyester, Elastane mix. They aren't (see image below).

Test subject: Waist 33", Inside Leg 30", Height: 5ft 8"
Test item: F-Lite's Megalight 140 Base Layer 1/2 Shorts (size = Large)
Kit Tests: Winter and Summer (multiple)
Disclaimer: None required (item not provided by manufacturer)


Materials: Polypropylene / Polyamide (Nylon) / Elastane 72% / 21% / 7%
Weight (Size Large, measured) 114g
Product Sizing Reference: 33" Waist = Large
Manufacturer RRP £24.00

Manufacturer's Page


Scramble Review



Introduction: What do we want?

Walking long distances, whether over flat or mountainous terrain, is a reasonably constant affair in terms of exertion and energy expenditure (unlike climbing which can be very stop and go). Since ones legs are doing the majority of the work, they're generating plenty of heat and thus even in sub zero temperatures we've not found the need for a thermal component to baselayer bottoms; if it's very cold just add a layer (see layering below).

The purpose of a baselayer is to move moisture and excess heat away from the skin and achieve a thermal balance that doesn't fluctuate too much throughout the day as conditions and activity levels vary. The most important factor when choosing baselayer bottoms is comfort, and that means: a) the avoidance of chafing, b) moisture wicking and by extension quick drying, c) breathable, and d) comfortable when wet, since in certain conditions no matter how skillful you may be, everything gets wet.


F-Lite Megalight 140s - The ideal length, elasticity and skin-tight fitF-Lite's Megalight 140 1/2 Shorts - Form-fitting, supportive and very comfortable

The F-Lite Megalight 140 1/2 Shorts (I'll refer to them as the F-Lite 140s from here) are made from an ideal mix of materials, they provide a skin-tight, "body-mapped" fit and are available, in our opinion, in the most favourable leg length. There are myriad options out there for baselayer bottoms, but the majority aren't really baselayers (they're often running tights / shorts or "compression" tights, or something that just looks like "this kind of thing" - the mix of materials says a lot); the F-Lite 140 however, certainly is a baselayer, here's why ...  

Cut, Materials & Performance

In my experience the half leg length is ideal for a baselayer. I've found that tight boxers tend to ride up into the groin and 3/4 length tights tend to ride up and bunch at the back of the knee. Form fitting, half-shorts on the other hand, tend to stay in place and don't pull, either from above or below, when the knee flexes.

There's not a great deal to these masterpieces of moisture management, but worthy of note is the waistband which went completely unnoticed. On some garments this can be an annoyance and dig in or feel awkward; not so with the F-Lite 140s.

Now onto the more interesting stuff, the materials. Since it's the fit, the form and the materials used that makes this item a proper baselayer.

The Perfect Combination: Polypropylene (Meraklon), Polyamide (Nylon) & Elastane

If I were designing baselayer bottoms, my choice and ratio of materials wouldn't be far off those of the F-Lite 140s: Polypropylene for its light weight, hydrophobic, thermal, and many other qualities (see below); Polyamide (Nylon) for its toughness and to aid compression and a decent helping of Elastane to provide the necessary stretch for a fitted baselayer.

So what's so special about Polypropylene? Quite a bit ...

The major element (72%) in the material mix for the F-Lite 140s is Polypropylene, from the standpoint of a lightweight baselayer it's hard to envisage a more appropriate material):

  • Lightweight: Because of its low specific gravity, polypropylene yields the greatest volume of fibre for a given weight. Polypropylene is the lightest of all fibres and is lighter than water. It is 34% lighter than polyester and 20% lighter than nylon.
  • Hydrophobic, thus quick to dry: The water absorption of polypropylene fibre is about 0.3% after 24 hours immersion in water, and thus its regain – the amount of water absorbed in a humid atmosphere – is virtually nil (0.05% at 65% RH, 21 °C.). Polypropylene is hydrophobic and will not absorb water in the fibre. Water “wicks” away from the skin and through the fabric to the face for quick evaporation.
  • Cold weather performance: Lowest thermal conductivity of any natural or synthetic fibre (6.0 compared to 7.3 for wool, 11.2 for viscose and 17.5 for cotton). Polypropylene fibres retain more heat for a longer period of time providing outstanding insulation and combined with its hydrophobic qualities keeps the wearer dry as well as warm. Polypropylene is warmer than wool, remains flexible at temperatures in the region of -55°C and recovers well from bending.
  • Microbially inert: Like other synthetic fibres – nylon, acrylic and polyester – polypropylene fibres are not attacked by bacteria or micro-organisms; they are also moth-proof and rot-proof and are inherently resistant to the growth of mildew and mold.
  • Abrasion: The abrasion resistance of polypropylene approaches that of nylon and remains high even when wet.

The F-Lite ML 140s have the same feel to them as Helly Hansen's polypropylene-based Dry Revolution baselayers, though are a little heavier and suitably for bottoms, more supportive. They are very form-fitting, almost compressive, yet have a nice soft interior feel. The inside is almost brushed (though not fleece-like), and provides the capillary action to move moisture through the fabric.

Inside the F-Lite 140s - stretch rib and waffle zones - an almost brushed innerOn the inside of the F-Lite 140s: stretch rib zones for support and waffle zones for warmth and moisture management

There is a seam that runs from the inner thigh into the crotch panel. However, on the inside this is barely noticeable and they may as well be seamless. Over various kit tests I've never had any chafing or discomfort while wearing them. They don't get clammy in the way polyester-based tights can, even when wet, and unlike merino-based (which for winter tops we're all in favour of) layers, the F-Lite 140s are more compressive, lighter, tougher and retain practically no moisture at all.

In winter we recomnmend merino wool for the top, but for bottoms, Meraklon is a superior option.

Finally, we are pleased to see there are no labels, instead the washing instructions and material mix is simply printed on the fabric inner.

F-Lite Megalight 140s - The actual material mixF-Lite Megalight 140s - no annoying labels.

Any Negatives?

None. At present, I can't find anything to fault them.


Conclusion & Rating

The F-Lite Megalight 140 Half Short Baselayers are made from an ideal mix of materials which combine for exceptional moisture management (wicking). They're comfortable when soaking wet and dry incredibly quickly. They don't get clammy when you're hot and sweaty or when you're soaked through, and after many miles in both the very hot and very cold, I've never experienced any chafing or discomfort. With a slightly compressive, form-hugging fit, they offer good support. At just over 100g they're light enough to carry a spare on very long treks (though probably not necessary), and to top it off they are free of stupid flappy labels. The F-Lite 140s are a superbly functional, practically seamless, year-round baselayer and the only thing we can't understand is why they're not better known. Treat your legs to a pair - they deserve it. The F-Lite Megalight 140 Half Shorts are Scramble's top pick in the Trekking Baselayer Bottoms category.


Product Images


Rating (out of 10)

RRP Value *

* The value score is derived from two factors:
1) Competitive Market Price (CMP). This represents our judgement of a competitive online price point if we were to stock the item. e.g. if we feel we would need to sell an item at 40% off (i.e. 60% of its full RRP) to be competitive, then our CMP score will be 6/10.
2) Customer Value Price (CVP). We then make an honest appraisal of the maximum price we would be willing to pay for the item (and we're mean). So if we'd pay 80% of its RRP our CVP score would be 8/10.
We then average the two scores to get our final value score, which in our example would be 7/10.


Cold Weather Add-on: Odlo's Cubic Tights (Active F-Dry Light Leggings)

F-Lite Megalight 140s under a pair of Odlo's Cubic Full Length Tights

Test subject: Waist 33", Inside Leg 30", Height: 5ft 8"
Test item: Odlo Cubic Full Length Tights (size = Large)
Kit Tests: Winter
Disclaimer: None required (item not provided by manufacturer)


Materials: Polyester (3D knitted construction) 100%
Treatments: Odlo Effect (Silver Anti-Microbial Treatment) -
Weight (Size Large, measured) 115g
Product Sizing Reference: 33" Waist (fitted / looser) = Medium / Large
Manufacturer RRP £35.00

Manufacturer's Page


The Perfect Winter Partner?

The Odlo Cubic tights lie somewhere between a traditional lightweight baselayer legging and the mesh designs "popularised" by longstanding Norwegian brand, Brynje. The basic idea behind the mesh layer is that, a) it's light because much of it is air, b) that air is trapped by other layers and acts as an insulating "air cushion" next to the skin, and c) it transports moisture and dries quickly. All of these qualities are present in Odlo's Cubic Tights (which, as of Summer 2018, are called "Active F-Dry Light Leggings" - so we have the F-Lite brand and the F-Dry leggings by Odlo ... F-in confused yet?).

The Odlo Cubic Tights, size large - a little long (for shorty) but not baggyThe Odlo Cubic Tights: Sizing up for winter

Odlo advertise them as a year-round legging and that's fair. They're certainly not a heavy thermal option, but in winter they pair extremely well with the F-Lite 140s, providing just enough additional protection while guaranteeing the wearer will not overheat, sweat like crazy and get wet and then very cold.

The Cubics are, like the F-Lite 140s, superb at keeping you dry and drying rapidly when soaked. For that reason, they are ideal in UK and wet Northern European winters - staying dry is the key to keeping warm. In addition they are extremely light at just 1g more than the F-Lite 140s for a full length legging (large = 115g).

Possibly an ideal fit for me would be a medium, but I only use these in the winter and a size large allows me to have them higher on the waist (sizing up doesn't make them baggy); I can then tuck in my baselayer top between the F-Lite 140s and the Odlo Cubics. I wear the Cubics underneath Scramble's recommended winter socks and this keeps everything in place nicely.

Darn Tough's Mountaineering Socks with the Cubics underneathDarn Tough's Mountaineering Socks over the Odlo Cubic tights

The larger size also means that there is no pulling when the knees flex. I've found this combination works a treat. At no time in the last, quite arduous Winter Kit Test (2018) did I notice any discomfort, whether in near-mountaineering mode (crampons, ice axe etc..) or when just putting in as many miles as fast as possible (on flatter icy terrain).

Although the windchill was some way below -20°C at times on the peaks, I never felt the need for additional layers. I didn't get hot and sweaty either. Another benefit of this F-Lite / Odlo combination, is that if the temperature does become uncomfortably low, one can switch them round and wear the Cubic tights underneath the F-Lites. This will make more efficient use of the air pockets and will improve insulation.

Zooming in on the Odlo Cubic's StructureA closer look at the 3D "mesh-like" design of the Oldo Cubic tights.

One of the really noticeable benefits of this combination was that because both the F-Lite 140s and the Cubics expel moisture so well, even after an ugly downpour on the latter stages of the test (when the temperature began to rise a little), the F-Lite 140s, the Cubic tights and the Akeleie Half Zip baselayers remained dry enough to be stuffed inside the sleeping bag (without the need of a dry bag) ensuring they were dry and warm for the next day. This has not been the case with previously tested baselayer bottoms, which have not shed moisture so effectively.

After 7 days (6 nights) of being outdoors continually, between -2°C and -10°C (at higher elevations) neither the F-Lite's nor the Odlo Cubics stunk. My socks, boots and a few other items did, but none of the next-to-skin layers - which is pretty impressive. We've seen above that polypropylene is pretty inert to mould and microbes. In many of their garments, Odlo use a silver treatment (a natural antimicrobial, antibacterial and antifungal) which they call "Effect Odour Control". It seems to work.

The Odlo Cubics - dry enough to gain entry into the Defence 4The Odlo Cubics remaining relatively fresh and impressively dry

It's been a long time coming, but this combination is going to take some beating. The F-Lite Megalight 140s all year round, supplemented by the Odlo Cubic full length tights in winter.

Additional layering

In certain conditions and depending on ones choice of trousers, an additional layer may be required. There are a ton of "compression", "baselayer" and running shorts out there that will pair well with the F-Lite / Odlo combo above. Personally I take these cheap and cheerful numbers from Precision along as a "just in case" spare (hopefully, as was case on the last Kit Test, not required) and as something fresh to travel back in when the test has completed.

Precision Training's lycra shortsThe F-Lite and Odlo baselayers pair well with standard training / compression shorts such as these by Precision Training

At Scramble we don't recommend any particular brand; the ones above are Precision Training's Lycra Shorts and cost under £10, but a quick tour of Amazon will present myriad alternatives (and customer opinions).

Layering options from Precision, Sub Sports, Under Armour and on and on ... take your pickAdditional layers from Precision, Sub Sports, Under Armour and on and on ... take your pick


Last Updated: 02/07/18  (to include the new name for the Odlo Cubics)


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