The 5PF is a single sheet of creased and scored corrugated. It features a 5th panel that commonly covers a side panel and is closed, usually with sealing tape. You can chose an alternative center seam closure.
It is a convenient way to package long items with a small diameter such as PVC pipe, rods, umbrellas, etc. It has the added benefit of extra cushioning at the ends to prevent damage to the product if the design of the product might push it through the ends of the box.