Fluid-filled products may consist of small or large chambers filled with air, water or other viscous fluid materials such as silicon elastomer or silicon or polyvinyl. The fluid flow from chamber to chamber or within a single chamber is passive in response to movement and requires no supplemental power. The term "air-flotation" is sometime used to describe interconnected multi-chamber surfaces such as those manufactured by ROHO, Inc. For air cushions, care must be taken to maintain the correct levels of inflation in order to achieve optimal pressure reduction. Under-inflation causes bottoming-out and over-inflation increases the interface pressure. For viscous fluid-filled seating surfaces like the Jay2 seat cushion (Sunrise Medical, Inc.) it is important to monitor the distribution of viscous material and manually move it back to the areas under bony prominences if it has moved away from these areas.