A variant of soft cover binding where the gathered pages are milled on the side of the spine to promote absorption of the glue and then glued to the cover. It is fast and economical but does not allow flat opening. A number of recently developed technique (polyurethane glues or PUR) are able to overcome this drawback and ensure a stronger binding, especially when papers having surfaces unreceptive to glues (pearly, gummed, etc.) are used.