Every year I take some long international flights.  DVT is a huge concern for me. (Search for DVT if you are not aware of this serious health risk.)  According to National Institute of Health, deep venous thrombosis (DVT) is the formation of a blood clot in a vein that is deep inside a part of the body, usually the legs.  The clot can block blood flow and cause swelling and pain. When a clot breaks off and moves through the bloodstream, this is called an embolism. An embolism can get stuck in the brain, lungs, heart, or other area, leading to severe damage.

Common techniques to prevent DVT include: taking aspirin to thin blood before long flights, wearing compression socks to avoid pooling of blood in the lower leg area, and getting up to move around often.  This pair of socks takes care of the second technique for me.  As an added benefit, the socks look nice when I get off the plane.