I bought a cotton canvass hat..."one size" and it's too small. Is there a way I can stretch it out a bit?

Question

There's no "extra" fabric to "let out."

Answer 1

soak in lukewarm water with fabric conditioner, Then find a ball the size you wish to have your hat, place the wet hat over the ball and leave to dry in the sun. Should work,

Answer 2

Soak it in warm water and laundry softener, hair conditioner will work also. Do not take it out until it is totally saturated. Dripping.

Find a bowl, pot or something that is a bit larger than it is and force it down over it. This should stretch it enough to fit.

Put the bowl and the dripping wet hat on a double thickness of towels to dry. It will probably take a couple of days.

Cotton will stretch and shrink. You can probably steam the brim with the iron after it is nearly dry, to make it look new again.