To warm the body before a massage, heating them to 130°F/55? to warm areas such as the stomach and haunch and use it as a warm neck pillow. The rounded, narrower edges can also be used to pressurize and knead particularly tense muscles and areas during treatments. 100% Natural Black Basalt; Excellent for holding heat for long periods of time; Rich with iron and magnesium. Shaped and polished by traditional handcraft, no wax, dyestuff, chemicals were applied. Size: 6' X 3.4' X 1.1' ', 4 pieces per pack.