I’ll give these a shot. Thank you very much!

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I’m not 100% sure, I think mesh? But it seems like the fabric from their tucking underwear varies from pair to pair. (From their FAQ: “When you place an order, the fabrics may not be the same as previous orders.”)

They have some bras and underwear specifically designated as bamboo, which is just as good as merino, but it’s seemingly only for their non-tucking underwear.

Oh, I hike day trips all the time while tucking. I don’t really notice anymore haha. I just don’t want to smell bad on a three-day trip!