feels true to size if you follow the other reviewers advice and size UP.  I am a womens size 9 and ordered the red fins (mens 9 to 11, I think).  They just fit.  The foot part is veyr soft silicone like feeling.  Works great.

Fits great and ;provides outstanding training technique.

Excellent training fin. I bought 'one-size up' based on an earlier evaluation which said they fit a little too snugly. Glad I did. They fit me well. Provide enough resistance for strength and speed without straining.

I love this fin it is great for training but have had difficulty with sizing i have the XS and also tried the S, I am a women's size 8 in a running shoe but the S fin felt a little too big and the XS feels a little too small, in the end I think the S fits the best.  I have a very narrow foot.

Product returned for larger size. I did order a larger size initially, as I had read reviews about the size issue, but still too small. I hope the next larger size fits.

CrossBlade fins work good. No blisters and enough resistance to get a good leg workout.