OUR MORPHSUITS ARE MADE OF 9% STRETCHY SPANDEX WHICH GIVES A 4-WAY STRETCH AND ALLOWS THE SUIT TO RETURN TO ITS ORIGINAL SIZE MAKING IT A SUPERIOR FIT AND MORE COMFORTABLE THAN OTHER PRODUCTS ON THE MARKET. IF IT DOES NOT SAY MORPHSUITS ON THE BACK THEN IT IS NOT A MORPHSUIT. WE HAVE FOUND THAT ONE SIZE PRETTY MUCH FITS ALL, BUT FOR A PERFECT FIT FOLLOW THIS SIMPLE GUIDE: IF YOU ARE SMALLER THAN 5'4" CHOOSE MEDIUM IF YOU ARE TALLER THAN 5'4" BUT SMALLER THAN 5'10" CHOOSE LARGE IF YOU ARE TALLER THAN 5'10" BUT SMALLER THAN 6'3" CHOOSE EXTRA LARGE IF YOU ARE TALLER THAN 6'3" CHOOSE EXTRA-EXTRA LARGE