Kraft for converting is specified by grammage, and the working range for cushioning applications spans a factor of two or more. Light paper expands more readily, produces more volume per kilogram and costs less per square metre. Heavy paper resists crushing better and survives more handling.

The instinct is to specify heavy paper for protection, and it is often wrong. Cushioning works by deforming; a paper stiff enough to resist deformation transmits the impact to the product instead of absorbing it. For light goods, lighter paper is not a compromise but the correct answer.

Where heavy paper earns its cost is in abrasion and repeated handling: a wrap that will be moved several times, a pallet interleaf that takes load, or any application where the material must survive the journey rather than only the first drop.

The practical method is to test rather than calculate. Run the product through the packing process with two grammages and drop it. This is a cheap experiment and it settles a question that specification sheets cannot.