Full flap or partial flap bottom?

Full flap

The flaps meet fully across the bottom. Loose hardware, castings and anything that can find a gap needs it. It is the usual choice for heavy loads.

Partial flap

The flaps leave a gap, which a slip sheet or liner covers. It is fine for bagged goods and bulky light loads, and slip sheets let a forklift push-pull the load. One used listing describes a 48 x 45 x 40 box as five-ply with partial bottom flaps and slip sheets.

Sleeve and tray

A separate base tray with a corrugated sleeve for the side walls; it can be taken apart for return shipping.

Why we ask

The bottom decides who can use a box, so every buy and sell request asks for it. See slip sheets.

Which one do you have

Turn the empty box on its side and look at the bottom. If four flaps meet in the middle with no gap, it is a full flap bottom. If the flaps stop short and leave a strip open, it is a partial flap. A third style, the sleeve and tray, has a separate tray that the sleeve drops over. The style affects how the box can be filled and emptied as much as how much it can carry.

Matching bottom to forklift

A partial flap bottom is meant to ride on a slip sheet, and a forklift with a push-pull attachment pulls the load by the sheet. A full flap bottom is meant to sit on a pallet. Send a box built for one to a dock set up for the other and the dock will have trouble with it. That is why the bottom style is in the form.

What the gap does

A partial flap leaves a strip of the base open, so product that would rest on the flaps instead rests on whatever is beneath the box: a slip sheet, a liner, or a pallet deck. This suits bagged and cartoned goods, which do not need a continuous floor. It does not suit loose parts, small pellets or anything that might fall through the gap.

Why the full flap carries more

A full flap bottom is a second layer of board under the load, and that layer spreads weight across the base. For dense products it is the safer choice, and for anything that could leak or sift through a gap it is the only one. The cost is that the box is slightly heavier and a little harder to flatten after use, which is a fair trade for a heavy load.

Checking a used box

Flaps are the first part of a used box to wear out. Look for creases that run across the board rather than along the fold, tears at the corners and tape residue that has pulled the surface off the liner. A bottom with good flaps behaves like a new one; a bottom with weak flaps needs a repair or a slip sheet. Sleeve and tray styles have no flaps at all, so check the tray for cracks instead.

A note on sleeves and trays

A sleeve and tray box is made of two parts that nest together. It has no flaps, so there are none to tear, and it can be assembled quickly. It is less common than flap bottoms, and its tray is the part to check.