• Overall Rating

  : 3-5 out of 5

The Mammut Lenni is the lightest shirt in our test and rolls up into a small bundle, making it a good choice for carrying in the pack on a multi-day walk when you want a shirt for travel or camp/town wear.

The thin polyester fabric is soft and feels pleasant next to the skin. It has a bio-based HEIQ Fresh FFL odour control treatment, a UPF of 50+, and is bluesign approved. Unsurprisingly for such a thin material drying time is very fast, and wind-resistance is quite low. The front fastens with buttons that are just big enough to use easily. The cuffs each have one buttonhole and two buttons so you can have them tight against the skin for protection or a bit looser for ventilation. The sleeves roll up easily but there are no tabs to keep them in place. The cuff buttons are a reasonable size and fairly easy to use but the button on the slit above the cuff is rather small and a bit fiddly. The hem is curved and just long enough to tuck into trousers and stay in place when I stretch.

This isn’t a shirt to choose if you like pockets. There’s only one and it’s quite small – my smartphone pokes out of the top. It fastens with a single small button, but that’s rather fiddly to use. The fabric has a silky feel and is comfortable against the skin. If it gets sweaty it doesn’t cling and it dries quickly. For really hot weather this shirt is excellent as it’s so thin and comfortable. I’d like to see another pocket and pockets that are bigger and can be closed more securely but if weight matters it is very light. The price is slightly high given the basic design.

How Chris tested

Chris is 5’8” and wears a size large. He tested these shirts in warm weather from spring into early autumn on high and low level walks in the Scottish Highlands. The shirts were weighed on his own scales.

This review was first published in the April 2026 issue of The Great Outdoors.