Blanket swelling occurs when the rubber surface absorbs excessive solvent or ink components, causing it to expand. This swelling is detrimental because it effectively increases the thickness or packing height of the blanket. This unexpected increase in thickness dramatically reduces the gap between the Blanket Cylinder and the Impression Cylinder, leading to significantly elevated pressure in the printing nip, which is the contact zone where the image is transferred to the paper.

The problem arises because this high, uncontrolled pressure physically forces the liquid ink on the blanket to spread excessively as it transfers to the substrate. This spreading deforms the halftone dots, causing them to print larger than their intended size—a phenomenon known as Dot Gain. A damaged blanket with nicks or uneven spots can similarly create localized pressure spikes, leading to inconsistent and unacceptable dot gain across the print sheet.