The only reason that I gave these socks 4 stars instead of 5 stars is because I am an 8.5 & the Small is a touch too short on a few of my toes.  I was afraid to go with a larger size because of needing to stuff the sock into the toe slots.  However, because of this, my toes do get sore after hiking with these socks.  I think I may be better off without & endure the sweaty feet.

Per the packaging, the fabric is 75% Coolmax, 22% Nylon & 3% Lycra.  The socks are described as ultra thin (designed as an ultra think interface), but they are not as thin as nylons or a women's trouser sock. I'd put them at around the same thickness as a thin men's dress sock.

The sock is further described as having AIS:Technology. (1) Anatomical 5 toe design - interface keeps toes dry and prevents blisters. Properly aligns toes for natural movement. (2) Arch Support - mid foot stability (tighter elastic band) eliminates bunching. (3) Vector Heel - precision stitching for custom fit prevents slipping. (4) Dual Welt Band - holds sock in place (this top band is the only thing you'll see when wearing this sock with your Vibrams).

Wash: machine wash warm & line dry.

Overall Impression:  I could definitely feel the sock inside of my Vibrams - the toes were a little tighter, comfortable enough at first, but my toes got sore after hiking for awhile.  They work well for sweaty feet, but the soreness over-rode the sweaty, so I ditched the socks mid-way through the hike. Some reviewers have written about cutting the toes off.  That may be a solution.  If I try it, I will post the results.