A calender for treating both sides of a paper web includes hard rollers and soft rollers. Working nips are formed between the juncture of each hard roller and soft roller. The roller stack can be loaded from one end, and preferably includes six to eight rollers. A changeover nip is formed by the juncture of two soft rollers or at the transition between two stacks. When using two stacks, each stack preferably has three to five rollers. At least one working nip has a dwell time of at least 0.1 ms. A heatable roller adjacent to the working nip is heated to a surface temperature of at least 100.degree. C. The roller stack is loaded such that an average compressive stress in the working nip is greater than or equal to 42 N/mm.sup.2.