Lightweight long-sleeve tee from their Layering Shirts and Tops range.
I got mine in XL, because of my super long arms, but was pleased to find it didn't swim on me, I assume this is due to the skin-snug fit they generally get worn with.
Some of the nice features of this shirt are that the ribbed collar maintains its shape, keeping it high and snug, without being constrictive. The soft fabric has given me no troubles with chafing, no matter what I've been doing, or how I've been layered.
Better yet, the antimicrobial blend of fabrics is designed to resist odor (proven after several days camp-side wear). It is also moisture-wicking and fast-drying, not through any coatings or washes, but through the propriety materials used. they wont wash out, or wear out.
Best yet, DRIFIRE gear is
made with no-melt, no-drip fabrics, so apparently they will not
melt or fuse to skin when exposed to flame or fire. This is excellent, as I really do not like being on fire. It's one of my least favourite things. Fire resistant clothes. This is a feature I'm willing to stake my skin on. Hopefully not one I'll put to the test though.
The seams are well placed, and flat woven, which also cuts down on the chafing risk, especially when laden down with pack straps or under a plate carrier.
For a long sleeve street-wear alternative to my other regular stand by, like the Truspec combat shirt or the short sleeve UnderArmor shirts I really like this shirt. Feels like a soft cotton tee, wears like a performance garment.