I bought a pack of these socks two months ago to replace some old socks that had begun to wear through.  I've been so pleased with them that I bought two more packs to replace my entire mismatched warm-weather sock collection - now I never have to search for a matching pair!  So far I am very pleased, though I will update this review if I encounter any durability issues.

I got the 'extended size' (12-16), and they fit my extended size feet (US shoe size 13) perfectly.  I use them every day with my Merrell Moab Ventilators (<a data-hook="product-link-linked" class="a-link-normal" href="/Merrell-Men-s-J86595-J86595W/dp/B006PFR5G6/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Merrell Men's J86595/J86595W</a>) while doing a considerable amount of running, hiking, and cycling, and I have never encountered a problem with them sliding around.  Perhaps the ill-fit described by other reviewers is just a sizing issue?

The entire sock is made of fairly thin cotton; the sock top is just this thin, breathable cotton liner, while the bottom, toe, and heel feature a thicker pile (looped cotton, like on a carpet or bath towel) for improved cushioning and absorbancy.