Just in case you think fleece has to be synthetic, Icebreaker calls the wool used for the Sierra Half Zip RealFleece. This has a smooth outer and a fluffy raised pile inner that feels very soft. The design is basic – just a sweater with a zip neck. There’s a tiny pocket on one sleeve that isn’t really much use and that’s it for features. The high collar is snug and warm and made of double fabric so it doesn’t sag. The zip isn’t actually half-length but is long enough for getting it on and off and for some ventilation. The warmth is somewhere between the thinnest synthetic fleece and a medium thickness one. I find it warm enough for sitting round at 10и_C and could only wear it under a shell when walking in much colder weather.  Like other merino garments it should remain smell-free on long trips. The weight is a little heavy compared with synthetic alternatives and the price is high but this is a lovely garment if you prefer wool to polyester.