How to Prevent Sandals From Causing Blisters. It's typical for new sandals to cause blisters to form on your tender feet. In fact, just about any new shoe is bound to do this. This happens because new shoes are still rather stiff and unyielding against your feet, causing parts of the shoes to rub back and forth against your feet as you walk, which leads to blisters. It usually takes a few days to one week for sandals to stretch out enough to stop causing blisters. In the meantime, there are steps you can take to prevent blisters from forming.
Wear socks with your sandals until they're sufficiently stretched out and worn.
Put an adhesive bandage across your heel where the back strap of your sandal rubs. This way, the strap will rub the bandage and not you skin. If your sandals rub other parts of your foot as well, place bandages in those places.
Glue or tape a small piece of smooth, comfortable fabric on the inside of your sandals in the places that are causing blisters. Once you've broken in the sandals, you can remove the fabric.
Ask someone with slightly bigger feet than you to wear your sandals for one or two days to stretch them out, so they won't continue causing blisters.
Dust talcum powder on the areas of your foot where the sandals are causing blisters. This will help the sandal parts slide comfortably over your skin. If you don't have talcum powder, baby oil also works.
Tape three to four cotton balls to your heel or other blister-prone area, and then slide socks over your feet. The more cotton you use, the more padding you'll have to prevent blisters. Just make sure you don't tape on so many cotton balls that you can no longer get your sandals on your feet.