This article is for use with the Best Fit Packing Algorithm
The default box tolerance has already been set to 10% in System > Configuration > Shipping Settings > Dimensional Shipping but some of the more fragile products need additional packing.
You can set a different box tolerance on a per-product basis with the ship_box_tolerance attribute. This is not assigned to the attribute group by default so this will need to be assigned.
Once assigned, simply assign the box tolerance to the product, as you would the default box tolerance.
In this example, this product will always have a box tolerance of 20%, regardless of the box.