Another component option for sub-atmospheric systems is the Symmetry System from Symmetry Prosthetics. I spoke to Ryan Colby, Director of Operations, to find out what it does, how it works, and what is different about it from other systems. Here's the scoop: The system, launched in February of 2010, is a socket, a liner, and a pump. The unique and proprietary components are the pump and the liner. There are two pump options. a passive pump and an electric rechargable active pump. The electric pump charge lasts about a week and has a maximum vacuum level of 18 mmHg. The liner is composed of a 6mm thick silicon liner with a 3mm skirt that acts as a seal. A sock can be used as a wick and tucks under the seal, allowing some adjustability by varying sock thickness. No external sleeve is needed and no portion of the liner is rolled over the brim of the socket. This increases the durability and eliminates the issue of tears casued by the brim of the socket on an external sleeve. Ryan pointed out that the Symmetry liner, unlike other liners with sealing rings, has an adjustable height of the sealing ring. You can put the sealing ring near the top, rather than near the disal end, of the residual limb. He said the tranfemoral system works best with sub-ischial socket designs. For more information, or You Tube links, contact Ryan Colbey at Symmetry Prosthetics.