I ordered one of these a while ago, and just ordered two more for my LBTC packs. Great fit and really help support the load and add to overall comfort. They are a sheet of plastic, with fabric surround to aid in the plastic "digging" into your pack fabric. The fit is great.
ATS Frame Sheet insert
The Frame Sheet Insert was designed specifically to fit the Lightfighter RAID, ATS RAID II and ATS Cobra packs, but will also fit packs of the Eagle A-III size. It is made from a sheet of HDPE, bound with edge tape and with an aluminum stay in the middle to keep it rigid. The Frame Sheet is recommended for assault packs that carry heavy loads. If you have to really load your pack, the Frame Sheet will be an increase in performance for you.
The ATS Frame Sheet is made in our factory in KY, and is lifetime warranted against defects in manufacturing and materials.
I purchased this framesheet for my London Bridge Trading Three Day Pack. The sheet fits perfectly and functions as intended but the fit/finish of the stiching that holds the edging and center stay in place are lacking and are coming undone. I don't think it will affect its usability but it is a bit annoying because the design of the pack allows the top portion of the sheet to be seen so I see it every time I open the pack. It's just my type-A personality and OCD nature but wanted others to be aware. If the framesheet will be completely sealed inside a hidden pocket as on most packs this is a PERFECT product at the given price point and makes the pack carry so much better with a heavy load.