Step 1: Get a Hat
Note: this hat was made from fake straw, but I'm pretty sure you can get real straw to work too if you change the glue recipe a bit.
Step 2: Shape the Hat
Once you have the shape picked out you can begin bending and shaping to get the look you are going for. For mine I wanted a simple cowboy hat, just the two ridges in the front with a curved brim. Using my fingers I dented in the front and squished in the sides to make the ridges and then held them in place with a needle and thread. When you have it just right it's a good idea to actually put the hat on to make sure it fits ok, also the look changes a bit when you actually wear it so that's another reason to try it on before you make it permanent. Getting the brim to curve up was easy, I just attached it to the hat at the point that would give it the amount of curve I wanted, again, using thread to do so. (ps- sorry the pictures are a bit blurry)
Step 3: Cover It in Glue
In order for the glue to penetrate you will need to water it down, I did 3 parts water to 1 part glue(I would use more glue and less water if it were real straw) mixed in a bowl big enough that I could set the hat in it and ladle the glue mixture onto it. The amount of glue mixture you use will depend on the size of the hat, for a small child's hat I used about 1/4 cup of glue and 3/4 cup of water and I had a little bit leftover when I was done.
Make sure the hat is completely saturated, especially on any spots where it's shape is being changed a lot. But don't forget to get the spots that aren't changing as well because the glue mixture will make the hat slightly shiny when it's dry and any spots that don't get covered will end up looking like they are dirty.
Now let the hat dry. It will take a little while, I did mine around noon and it was still wet when I went to bed but the next morning around 8 it was good and dry.
Step 4: Enjoy!
Yesterday I found a hat that was exactly like I was looking for, but it was way more expensive and the cheap dollar store hat seems to be holding up to the abuse just fine. It has been pulled and squished and still holds its shape.
Thanks for reading and I hope this comes in handy for anyone wanting to make a costume on a dime!