An as-manufactured multi-wall sack that comprises an inner pouch 5 and an outer bag 7 is disclosed. The sack has a top end that (a) is open in the as-manufactured form of the sack so that the sack can be filled with product via the open end and (b) is formed so that it can be closed to form a top block end. The as-manufactured form of the sack comprises pressure adhesive that connects together the inner pouch and the outer bag at the open top end of the sack. The as-manufactured form of the sack also comprises heat-activated adhesive on sections of the outer bag that adhere to other sections of the outer bag as part of the sequence of steps to close the outer bag. An apparatus and a method for closing the as-manufactured sack are also disclosed.