We bought these socks in L on July 2022 & they quickly became my darling's favourite pairs. He wears 11 in running shoes. He usually runs 7 - 10 km every time in hot humid weather (tropical). He also has some thicker socks from other brands & a Feetures pair (which for him are too thin & he prefers these because of more cushion) & these running shoes: Adizero Adios Pro 2 (these shoes stained the socks, noticeable on the pics attached), Nike ZoomX Vaporfly NEXT% 2, New Balance Fresh Foam 1080 V12 (very worn out already) & Hoka One One Bondi (go to shoe for current runs).Since I've seen him leave them to air dry after runs to wear them again the next day (he do loves them... & they do dry super fast & in general don't hold bad odours), I bought him another pack. Check the picture to see the old pair (worn very regularly since July 2022) & the new pair to see how they wash (line-dried).Since my darling loved this brand, I also bought myself a pack. I thought I would confuse his with mines when washing them, but they have the size (L & S) in the inner rim. I wear 7.5 in running shoes & I have very narrow feet. I run as well but not to that level, only 5 - 7km each time. I've bought these other pairs: Brooks Unisex Run-In 3-Pair Pack, Under Armour Unisex-Adult ArmourDry Run No Show Tab Socks (see the pics). Those pairs are noticeable thicker, while these Monfoot ones fit allright for narrow feet & have good cushion.Overall, two regular runners recommend these socks.I hope it helps.