A Stiffened Brim has an interlining layer in some stiff material, usually with Millinery wire along the edge. This gives the brim a very smooth look and a degree of shapeability. (Note: Millinery wire isn’t really exactly period for most of history. Um, at all. Sorry. You can buy it online through
www.JudithM.com)
Traditional Millinery uses buckram for this interlining,
which is great so long as you never, ever get it wet. A lot of hats made for ren faire purposes use plastic canvas as an interlining (an idea that nearly caused my Millinery teacher to faint) — great, but kinda heavy, and hard to go through with a sewing machine, and it can show through the outside of the hat if you’re not careful or the hat gets wet. Trust me, because I’ve don this many a time. A double layer of craft felt sized with regular Elmer’s White Glue will work in a pinch. I’m going to use a Pellon product called PelTex, which is a super heavy duty sew in interfacing. It’s expensive, unfortunately — 8$/yd, last I checked, but you can get a lot of brims out of a yard.
As well as your interfacing, you will need about a yard of Millinery Wire, a cutting pliers, your Basic Brim Patterns (both with and without seam allowance), enough fabric to lay the brim with seam allowances out twice, thread, sewing machine, hand sewing needles (preferably a small curved one), scissors, pins, and some patience.