Blanket pertains to the thick rubber mat on a printing press that transfers ink from the plate to paper.

See also:
"Blanket" is in the UNSPSC Code "42191906"
  Blanket or solution warmer cabinets

Ref: 122115/2006-09-19

Blanket is described as a fiber-glass or rock-wool insulation that comes in long rolls 15 or 23 inches wide.