Box selection runs from outside in, because the outer size has to fit the pallet and vehicle and the inner size has to fit product and coolant. A box that does not fit the pallet carries empty volume on every shipment.
| Box base (mm) | Layer of a 1200 x 800 mm Euro pallet |
|---|---|
| 600 x 400 | 4 boxes, no gap |
| 400 x 300 | 8 boxes, no gap |
| 500 x 400 | 4 boxes, a 200 mm strip left empty |
The inner size is the outer size minus wall, base and lid thickness. The GEBHARDT Thermobox EPP measures 600 x 400 x 320 mm outside and 538 x 338 x 257 mm inside, 46 litres: about two fifths of the 76.8-litre outer volume goes to the walls, which come out at 31 mm at the sides. At the same outer size a thin-walled box gives more litres but protects for less time, because heat flow is inversely proportional to thickness. Thick walls where time is critical, thin where volume is.
Volume the product does not fill is air that warms quickly and wastes coolant; the remaining space is closed with filler. Include height in the sums: the internal height of the pallet and vehicle sets how many layers fit, and one lost layer shows in the number of trips. Fewer sizes simplify stock; for each product check lid closure and temperature record on a box loaded with the actual packaging and coolant.