Kappa number measures residual lignin content in the pulp after cooking. A lower kappa number indicates more complete delignification, which affects the pulp's bleachability and strength properties. For unbleached grades used in packaging, buyers specify kappa number to ensure consistent bonding strength and to predict how the pulp will perform on the paper machine.

Coniferous (softwood) fibers are significantly longer than hardwood fibers, which translates into superior tensile and tear strength in the finished sheet. This makes unbleached coniferous kraft the preferred furnish for demanding packaging applications like grocery sacks, cement bags, and heavy-duty linerboard, where hardwood pulp alone would not meet strength requirements.