Mountain Equipment's Integrity Zip T is light, warm and stretchy base layer with excellent wicking properties along with a venting half length zip and chest pocket.
Mountain Equipment says:
A close fitting, low bulk zip tee for climbing and trekking use.
Delta fabric moves moisture rapidly to make it ideal for strenuous climbing use. A short neck zip gives added ventilation when the sun hits the final pitches.
Mountain Equipment's Integrity Zip T is light, warm and stretchy base layer with excellent wicking properties. It could also work as a mid layer though it is slim fitting. The half length zip allows some venting if you are working hard. Small items such as phone can be kept secure and accessible thanks to the zipped chest pocket.
Mountain Equipment is a member of the Fair Wear Foundation meaning they are committed to giving factory workers safe, dignified and properly paid employment.