I decided that I’d like the back panel of my ULA Ohm to be a little more structured and less flexible. The obvious thing to do was to add a sheet of HDPE to the foam sheet (a cut down Karrimat) that I was using. I ordered some 500mm x 250mm HDPE sheets from Direct Plastics. The sheets are so cheap I ordered 3 x 1mm and 3 x 1.5mm sheets, in case I want to use the HDPE for any other projects.
The sheets are almost exactly the correct shape. I had to cut the top corners off, which was easily done with a pair of sharp scissors. I used the 1.5mm thickness sheet as I felt it gave a little more rigidity and attached it to the foam pad with some duct tape. The weight is about 160g (HDPE sheet).
I’m pleased with the outcome. The back panel no longer bulges when you pack the sack and I can guarantee that no objects will jab me in the back. I’m pretty pleased with it. I think it will make the pack more comfortable, together with my hip belt mod. I had been thinking about getting an old style Gossamer Gear Gorilla pack (if I could find one), but I’m not sure I’ll bother as the Ohm is basically the same but with better quality materials.