Work on wide hat brim. will steam or hair dryer work to activate starch. what temp starch need to stiffen.

When I used this on my hats and was trying to remove any creases or wrinkles I would use a steam iron along with the starch. Make sure to use it flat on the surface of the brim, because if the brim has a fold at the edge it will create dimples in the brim because of the space between the iron and the fabric, so if you have a rolled edge on the rim just use the tip of the iron to get all areas of the brim. The steam will dampen the fabric so once you're finished ironing it be sure to shape it then set it aside to let it dry, and while it's drying keep an eye on it and reshape it a time or two if necessary until it's completely dry. If done carefully the hat will look brand new!

What are the ingredients? Does this product contain formaldehyde, phenol, or pentachloride? Is there a natural alternative, or will I need to diy?

I suppose what ever starch contains. The bottle says it Contains more than 97% nature based and biodegradable ingredients and does not contain propellants. I use it for all my quilting needs.

can you pour this into the iron instead of water?

No, it could gum up the iron’s spray holes. Spray starch on fabric & pour only cold tap or distilled water, according to iron manufacturer instructions.