Wet the cotton sweater with water by dunking it in a sink or bathtub. Squeeze out as much water as possible after wetting the cotton sweater.
Lay a blocking board on a tabletop or stable work surface. Spread the sweater out on the blocking board.
Stretch the cotton sweater out to the desired shape and size, smoothing it with your hands as you stretch. Secure the stretched cotton sweater in place by pinning it to the blocking board with straight pins. Pinning will prevent the cotton fibers from shriveling during drying.
Give the cotton sweater a light spritzing with water from a spray bottle after stretching and pinning. Allow the cotton sweater to air dry, thoroughly.
Remove the pins after air-drying and slip on your cotton sweater. Repeat the process if your cotton sweater needs further stretching.
If you have a clothes steamer, you can steam the cotton sweater after pinning. Steaming the pinned cotton sweater until it is dry will eliminate several hours worth of drying time.
Blocking boards are padded work surfaces, sold in sewing, fabric and craft stores.
Do not remove the pins before the cotton sweater dries. If you do, the cotton fabric will revert back to its original state.