Crocheted hats that are made from natural fibers like wool or cotton or flax or in a blend of the fibers should be handwashed in cool water.
Use a mild detergent and allow the cap to soak for twenty minutes, agitate gently - never squeeze or wring. Rinse thoroughly and allow to air dry flat. If the hat is misshapen, reshape as it lies flat and allow to dry.
Iron only if you must
If you need to iron to get all the wrinkles out, set the iron on the lowest heat setting suggested for the yarn. Place a slightly damp cloth, such as a clean cotton dish towel, on top of your crocheted piece before ironing. Never allow the iron to come into direct contact with the yarn. Excessive heat can ruin the integrity of the yarn fibers.
When you're not using the item, whether it's a sweater or tablecloth or anything in between, never hang crocheted items. Hanging stretches out the stitches, and the damage can't be reversed.
If items are to be stored for any length of time, invest in some acid-free tissue paper. Place the paper between the folds and around the outside of the piece. This ensures that the piece stays clean and dust-free and helps preserve the yarn fibers until you bring it out again.
Always put your items away clean. Time in storage allows stains to set.