When I wear it on a day when it has suddenly cooled down even though it is October. Even though it has short sleeves, it is as warm as a long-sleeved shirt. It's not thin, but it's not particularly thick, though. You can feel the warmth of wool.
Winter underwear for people who sweat outdoors in the midwinter, such as winter mountains and skis. Of course, you can wear it even in the city. The material is 80% merino wool and 20% polyamide (nylon). The tags say US XL and EUR 2XL. In Japan, it is between 2XL and 3XL. It is long and covers your butt completely. It has short sleeves, but it is long and comes close to the elbows. If you wear a short-sleeved shirt on top, the sleeves will stick out.
With the arrival of cold winter, a thermal inner shirt is what is needed especially for someone like me who is a bit chilly. And it is even more useful for those who love trekking or who go to high altitudes. This shirt is simply perfect.