I've been struggling for awhile now with sizing for wool felt hats. I've used an aerosol, which was okay, but eventually the hats lose their shape. I've also used a gelatin solution, which I really like, but it will often leave shiny, uneven splotches everywhere. Would love any advice I could get on technique or products or whatever.
Lots of people work with a variety of stiffeners. I use "Aileen's Fabric Stiffener" It is available at JoAnn's fabric in the US. I don't know if it's available anywhere else but I do know that JoAnn's has a web site. There are no fumes that I can tell. This is what I stiffened my felt hat with and it came out pretty well. I use about 3 parts water to 2 parts stiffener in a spray bottle. You then brush it around to cover all of the felt. I have used this to make chiffon board stiff and it really works well. It will leave spots on pale thin fabric but it doesn't seem to have a problem with felt.
You may want to reverse that recipe. Three parts stiffener and two parts water. I made a batch of stiffener using the above recipe and even after stiffening it twice the hat wasn't stiff enough to wire and trim.