Grammage Ratio
Paperboard mills construct multi-ply substrates with mechanical pulp cores to achieve high structural stiffness at lower overall sheet weights. High bulk folding boxboard designates a multi-ply packaging grade exhibiting a high caliper to basis weight ratio, typically exceeding one point four cubic centimetres per gram. The board features bleached chemical pulp outer layers for high-fidelity printing and a thick mechanical pulp center for bending resistance.
Grade designations lose applicability when basis weights drop below one hundred and eighty grams per square metre or when sheets contain only chemical pulp.
Stiffness Behavior
Layered sheet structures maximize stiffness by placing high-modulus chemical fibres at outer surfaces and low-density mechanical pulp in the center ply. Utilizing high bulk folding boxboard allows packaging specifiers to reduce paperboard grammage while maintaining carton compression strength requirements. Lower sheet mass reduces shipping costs and total raw material consumption across retail packaging supply chains.
When converters replace solid bleached sulphate with high bulk grades, package structural performance remains stable while total fibre consumption drops by up to fifteen percent.
Converting Limit
Mechanical pulp cores exhibit lower internal bond strength than solid chemical sheets. Excessive creasing matrix depths split internal plies during package folding operations.
