Outside Material: Outside is suede, sole is the same rubbery/plastic-y sole that are found on other fit-flops.  There is a light layer of rubber on the bottom of the boot giving it just a tad of traction (but ironically the traction on this FitFlop Mukluk feels more 'secure' than the traction of the FitFlop  snow/moon boot).

Inside Material: The inside is the only thing that I would like improved.  The fuzzy material that coats the entire inside of the boot (not just the top portion that folds over.  The entire boot all the way down to the toes is covered, which is good) is made of some synthetic faux-animal fibers.  While they do their job by giving off great warmth, I found that for somewhere around 140 bucks, I would have liked real fur.  But maybe that would make the shoe far more expensive???  Plus, even at the very ends (i.e. tops of the boot, where if you had them pulled all the way up you would see the first layer of the faux-fur) the faux-fur is already visibly falling out, sort of reminding me of the way that sweaters look once they pill.  When I first opened the box I was disappointed because a few small clumps of the faux fur were already falling out, so I was just waiting to see how long these would last.  I've now had them around a month-and-a-half and except for the tops, the faux-fur hasn't really continued to fall out.

Size: I find these run TRUE TO SIZE.  I ordered a size bigger b/c I had read they ran small, plus I have the FitFlop VanGoghs and those fit me exact with no slack - so I was worried if wore these FitFlop Mukluks  with socks they wouldn't fit (although they suggest it, who would wear no socks in weather that calls for these boots is beyond me).  I ordered the size up, and they are much too big (even when my feet are swollen, which they often get). I wish FitFlop would change their ways and create half sizes already.  The (little tiny) insert that came with the boot said that these are supposed to be worn without socks and should fit like a glove, although be warned that you should keep your toenails trimmed so you don't poke through the suede.  (Which also seemed odd to me.  Why would a delayed visit to the nail salon make a hole in your shoe?  Is the quality of the boot that bad?  I can't comment on the likelihood of poking a hole through as...I haven't done so).

Overall: These boots are great.  The color is great - I got the Chestnut (light brown) and it looks really nice-- color is represented nicely in the photo.  They are so cute.  And comfortable.  Even though they are big for me, I loved them so much that I didn't have the heart to go through the whole return/exchange process, and so far I haven't been let down.