A custom box solves fit
Stock boxes come in fixed sizes. An item that is long, unusually proportioned or too close to the walls of a stock carton may need a box resized or built to provide appropriate clearance for protection.
Double-boxing adds separation
A double-box system puts a protected inner carton inside a larger outer carton. Cushioning between the two cartons helps keep the inner package away from direct outside impacts.
More cardboard is not automatically safer
A package can still fail if the item moves inside the inner box, the outer box is too weak, the cushioning is compressed incorrectly or the package is too heavy for the materials being used.
The shipment decides the method
Weight, fragility, value, carrier network, destination and available original packaging all influence the final packing recommendation.