You may have seen the characters “mmHg” next to the compression level of a stocking, such as 20-30mmHg. This stands for “millimeters of mercury.” The equipment that measures the compression strength of a stocking uses a gauge filled with mercury, much like a household thermometer uses mercury. The more mercury displaced, the stronger the compression. When you see 20-30mmHg you know that product has been tested and provides that amount of compression.
Today’s compression stockings are made in a variety of fabrics. Many people assume that a sheer fabric will not provide as much compression as a thicker, opaque fabric. This is not true. The sheerest of fabrics will provide the same amount of compression as the thickest of fabrics, if they are rated with the same mmHg. The sheerness or opaqueness of a fabric is a result of the yarns and the weave that are used in the construction.