The Sillian t-shirt from Odlo is unbelievably comfy - the 4-way 'peached stretch' nylon is soft on the skin, lightweight and has superb moisture management which wicks away perspiration as you heat up and dries very quickly, even if you're drenched in a downpour.
The design of the Sillian is deceptively simple, with fine stitching at the seams and openings for comfort, as well as shoulder seams off the top of the shoulders, out of the way of backpack shoulder straps to avoid chaffing.
The Sillian has a UV protection rating of 50, protecting you from the sun while outdoors all day, and a long-sleeved version is available for even more protection and extra warmth.
At first sight the Sillian seems slightly expensive as a 't-shirt' but helping to justify its price is its year-round versatility, with its base-layer performance making it a good next-to-skin layer either on its own in summer or under other layers in winter. Add to this a high build quality and excellent performance and this is a worthy investment.