Immobilizing device for restraining a body portion or limb, comprising an air impervious pliant bag, e.g. of urethane coated nylon fabric, a plurality of lightweight expanded beads, e.g. polystyrene beads, preferably of relatively uniform large size of a diameter greater than 5 mm placed within the bag, and a self-closing valve communicating with the interior of the bag for evacuating air therefrom. The beads are free to be moved and accumulate in those areas where support is most needed. When the interior of the bag is evacuated, the beads are compacted by the collapsing bag and deformed into a rigid construction around the body member for support and restraint thereof. The bag is shaped to completely surround the body member to be supported and releasable strap means preferably are provided to maintain the bag in wrapped position around the body member before and after evacuation. After a period of use, introduction of air into the interior of the bag through the valve again permits freedom of movement of the beads and causes the device to collapse, and the device can then be removed from around the body member by releasing the strap means.