The detachable lumbar pad cushion is compatible with M2 and P1 hipbelt, providing extra support to your lumbar and lower back. 

Lumbar pad in use
Step 1 Let the flat side of the lumbar pad out
Step 2 Insert one side of the hipbelt into the webbing loop on the lumbar pad
Step 3 Position the lumbar pad in the middle and then do the same for the other side of the hipbelt