I received these shoes and wore them the next day with no issues.  Even though the sole feels thick it did not cause my any issues that would require a break in period.  The rubber smell is pretty strong so be sure to take them out of the package as soon as you receive them to let them air out.<br /><br />On a side note, my cat also gives them 5 stars because of the apparently catnip flavored shoelaces.  His new favorite thing to chew on when I take them off with out putting them up!