a device and method prevent damage to an anti - extrusion device on a tool , such as a plug or a packer , prior to and during setting of the tool . typically , the upper or outer edges of the anti - extrusion device are relatively delicate . a reinforcing band on the device &# 39 ; s sheath strengthens or armors the upper or outer edge of the anti - extrusion device so the anti - extrusion device may be protected while running the tool into the well or casing . longitudinal slots on the sheath allow the sheath to expand at least partially with the expansion of the sealing element , while the reinforcing band resists expansion of the distal edge of the sheath .