I have another pair of women's Mucks- the breezy- U.S. size 8 (I am a size 8). Those boots I could wear all day in the woods on the first day. No breaking in at all. These women's wetlands boots I was afraid to wear a 10 hour day in the field. Within 15 minutes of wearing them I could feel the boots rubbing against to top of my foot. (Wearing thin socks.) I switched back to my old Mucks. From the outside the boots look larger than an 8. Length of the foot fits fine. But the top of the foot concerns me. I'm hoping to break them in on a few shorter trips. I hope that the insole will give a little. The top of the boot fits great, which I have a larger calf. If you have really slender calves I am not sure if they would fit snug to keep water from getting in the boots. Overall, I hope the boots give a little. Not sure if I have and abnormally large instep???