LAST YEAR, New York designer Molly Moorkamp made an audacious decision. She replaced her namesake line’s merino-wool-blend sweaters with cotton knits, which she now sells year-round—even in winter. The 100% cotton styles range from a cold-weather cable-knit turtleneck to a four-seasons-friendly striped option. Her knits, she claims, have proven more popular since she made the switch, possibly because cotton costs less than most wools and is easier to clean at home. Plus: “The customer knows what cotton is going to be,” said Moorkamp. There are no surprises. “And nobody has said, ‘I miss the merino.’”

Most people view cotton sweaters, unfairly, as summer-only options. When fall blusters in, they flock to cashmere- and merino-wool knits, convinced ovine fibers make superior fall and winter fare. But if you pick the right ones, cotton knits can hold their own in cooler months. Some of this season’s thick-gauge styles by brands including Alex Mill, Kule and Buck Mason are so cozy, they might have impressed Roald Amundsen—the guy who discovered the South Pole.