16 fig9 shows an alternative embodiment of the cell structure of the sleeve where the inner part 30 and side walls 26 are pre formed in an open box configuration by vacuum forming a single sheet but cut to allow excess material adjacent to the welds to make a baggy configuration the pre formed open box is then welded or bonded to the outer wall 18 fig1 shows an alternative embodiment of the sleeve of the invention where the sleeve 2 comprises three adjacent cells 8 10 12 the external edges 28 of the cells are not provided with side walls but the internal edges of the cells are provided with side walls 26 the invention will now be illustrated by the following non limiting examples two adjacent cells of a device similar to that shown in fig1 were the subject of a finite element analysis to simulate the pressure profile experienced by the limb when such a device is used the analysis was conducted assuming a cell construction such as that used in fig3 and compared to a cell construction such as that used in fig7 where the cells have side walls the analysis was conducted using abacus uk ltd software version 6 41 fig1 shows the profile generated for the device of fig3 where the cells are of a simple bag like construction the pressure distribution is uneven showing peaks at the edge of each cell which fall rapidly to a large area of zero pressure between the cells the pressure is also depressed at the centre of each cell by contrast the pressure distribution shown in fig1 for the device.