My hat is too loose...
1) Blocking the hat smaller The idea behind this advice is that if you wet the hat and then block it smaller, the hat will stay that way. It is true that thoroughly wetting a too-loose hat, then firmly yanking it lengthwise will make it both longer and narrower. It is also true that pushing the fabric together and drying it in that scrunched-up position will make the hat look smaller. Yet, sadly, although blocking can do many magical things (such as make your knitting look more professional by evening out the stitches, or opening up lace) it cannot make things smaller. Logic will tell you that any "smallerizing" you were able to achieve by blocking will be undone as soon as you put the hat on and wear it. Plus, blocking really works best on wool, anyway, so if your hat is made of anything else, fuggedaboudit, as they say in New York.
2) Felting the hat smaller The idea here is to shrink the hat by felting it smaller. It is indisputably true that felting will shrink woolens. However, imho, this advice is ill-advised. Felting is a wild and uncontrolled process which goes very very fast when it finally happens, so getting the hat to shrink "just so" would be a matter of great luck. A too-small, too-short, too-stiff object--a sort of a felt bowl--is just as likely to be the result of the experiment. It is true that there are commercially felted hats, and even commercially-made felted jackets, but fitted felted garments are cut out of sheets of felted knitting and then sewn together. Home-made felted clogs are a popular exception, as are felted mittens, but clogs and mittens are meant to fit loosely--it is not necessary to have them sit "just so" around one's feet or hands, as a hat must sit around one's brow.
The one almost-exception to all this occurs with superwash wool. Of course, the whole POINT of superwash wool is that it does NOT felt, yet many knitters may not realize that putting this sort of yarn into a dryer helps it regain its bounce and size--a superwash hat laid out to dry will be much bigger than one machine-dried. So, while throwing a superwash hat into the dryer is not felting per se, it is "shrinking" through using a clothes drier--an almost exception to the don't-felt concept.
Now we come to two ideas which DO work.
1. Lining the hat This idea is 100% guaranteed to work 100% of the time. The idea is to make a lining--either a full lining or a headband style lining, which does fit your head exactly as you would like. An excellent fabric to use for this lining is polar fleece. Polar fleece is stretchy, non-itchy, comes in various weights, and best of all, it does not fray (and so, does not need to be hemmed). The lining is then sewn inside the too-large hat, easing the excess fabric of the hat to the lining, one little stitch at a time. Because the lining was made to fit your head exactly, the resulting hat must also fit your head exactly. There are more complete details about the process in these two posts:
Lining a hat, headband style
Lining a hat, fully-lined style
2. Elastic Sometimes, lining a hat will not work, either because of its style--a slouch-hat, for example, with no real "band" around the forehead, or because a sewn in band is not a good fit for the style of the hat--a lacy cap, for example. For such hats, you may wish to consider thread elastic, worked into the edge for several rows or rounds. The how-to can be found in this post on tightening up socks--scroll down a bit and you will find thread elastic discussed.
This post the fourth in a series on garment correction. The other posts in this series are:
Part 1: My sweater is too wide
Part 2: My sweater is too long, my sweater is too short
Part 3:My sweater is too tight under the arms/at the bust/chest--the magic of gussets
Part 5: My sweater slips off my shoulders
Part 6 (still to come): My sweater is too small around my middle
You have been reading TECHknitting blog on "my hat is too big!"