On the extreme end of both ends of the spectrum, you have outliers that cater to more specialty applications. Featherweight base layers are almost exclusively used for distance runners in need of something to keep off late year chill and biting winds, but still keep them dry and unencumbered. The Härkila Heat Long Johns are a pair of long underpants with built-in heating membranes that can be set to exactly the temperature you desire. This makes them an excellent choice for a wide range of hunting and outdoor activities in the cold weather. Note that the power-bank needed to heat these Long Johns is sold separately. Because of their extreme insulative properties, these thermal underwear won’t breathe at all, and any amount of prolonged exertion is likely to result in an uncomfortable sweaty mess.

If ever something was made for winter, it was thermals. If the thought of stepping outside fills you with dread, even when you’re wearing a coat, thermals are the answer. Put them on over your underwear, and then layer your clothes on top for a day filled with warmth, comfort and joy. A sound sleepHe says they are brill bought him the long sleeved top so he nice and warm great buy would defo buy again Lightweight thermal underwear as a rule will always be more effective at keeping you cool and dry than anything heavy. Beyond this, any difference is strictly material–and different textiles will have different performance impacts based on their inherent qualities. There’s a reason that there are so many die-hard merino fanatics out there, and a reason why merino tends to be on the upper end of the price spectrum in all applications. Pros

Long johns and by extension, other base layer categories, almost always have their fabric weight rating listed somewhere. The categories might not be hard-cut but are a dependable place to start your search barring no strong specific preference. Bringing a “best of both worlds” attitude to the table, blends tend to be among the most expensive and performance oriented options out there. Pros You might opt for midweight long johns as something to wear around the fire when fall camping. Patagonia Capilene is a great thermal underwear for this. Not quite as light or layerable as the diminutive lightweight category, they’re nonetheless still a fine choice underneath uninsulated snow pants or a waterproof shell when you’re out and about.The traditional fit and classic ribbed fabric shape to your body’s natural contours for a more comfortable fit, keeping you wonderfully warm all winter long. Rated 0.45 tog, these men’s thermal long johns will keep you cosy, with a seamless fit for layering under your clothes. In many ways Merino is the highest quality option, tending to really drive the price up–it has the unfortunate consequence of also being among the least durable of the fabrics.