The description says ultra light and base layer but that's subjective with no ability to touch/compare. I have old Merino wool sweaters and I know it's not a sweater but I thought the top was a little thicker. Otherwise, the average size will do. If you usually go up a size like I do with some tops, you might want to reconsider because of the sleeve length. Will see how well they hold up and may buy again when more colors become available.
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