It was cotton, not that horrible polyester in bag that you get at walmart, so it was comfortable.  My daughter loved it! I can not emphasize that enough, she LOVED IT!  The apron shoulders were a little big, but I looped the tie in the back through them to pull them in.  My daughter is 4 and very tall and skinny, so for a chubbier toddler it may not have been too wide.  It was a little pricey, I felt it was worth it, my husband had different thoughts, haha.  Overall it was a huge hit!
UPDATE 5-29-15
We still love this costume, it has been worn so many times for costume parties, book day at school, a parade, it's awesome! I am so glad we bought this costume, we seriously got our money's worth on it.