slip sheet
A sheet inserted between freshly printed pages to prevent them from sticking together.
slip sheet: barrier against wet ink transfer
A slip sheet is a thin, uncoated or lightly coated sheet inserted between freshly printed pages as they stack in the delivery pile of a printing press. Its job is straightforward: prevent the wet ink on one printed surface from transferring to the back of the sheet above it, a defect called offset or set-off. Without slip sheets, ink smudging and blocking (where sheets stick together) ruins finished product and wastes time separating damaged sheets by hand.
The material varies by application. Newsprint slip sheets are typically inexpensive kraft paper, uncoated and absorbent, ranging from 40 to 60 gsm. For higher quality work, coated slip sheets made from clay-coated or sized stock (70 to 100 gsm) reduce ink transfer better and feed more reliably through automatic handling systems. Some operations use silicone-coated release papers for jobs where the slip sheet must not stick at all. The sheet sits on top of each printed page, creating a dry barrier between that print and the wet ink of the next sheet as it lands.
Slip sheeting is most critical on high-speed offset lithography, especially with heavy ink coverage or dark solids. It becomes unnecessary on many digital presses, where ink dries instantly, and pointless on dry-toner systems. Sheetfed offset presses typically deploy slip sheets automatically at the delivery end; web presses handling cut-and-stack output may use them as sheets are tallied. The choice of slip sheet weight and coating affects press speed, paper cost, and waste rate, since every slip sheet becomes scrap unless recovered for recycling or reuse.
The term reflects its function: the sheet allows stacked pages to slip past one another without sticking. It is distinct from a waste sheet (a blank sheet run through the press to prime the unit and stabilize ink flow) and from interleaving tissue used for protection during storage or transport. In older manual operations, printers cut slip sheets from cheap stock; modern pressroom practice typically buys them pre-cut and sized to match the job.