Thermoskin is comprised of With the chest strap open to the front, place the shorter strap across the chest and feed the longer strap under the opposite arm and through the buckle of the short strap, pull taut until comfortable.
Don't bother if you are larger build, or not a Gym Junky.
This product says 1 size. this is not correct. if you have bigger Biceps, it will not wrap around them plus the Hook & Loop has the hard hook side against your skin sop its unwearable under clothing. If you also have a large chest the strap is not long enough to go around you, also the hook side of the fastening for the strap is also sharp on edged so it cannot be worn against bare skin.
So, if you have a 6 Pack its ok for you, if you are not looking like a fitness Gym junky or larger person this stap will not fit you.