Taking all or parts of a modern sewn straw hat and reshaping (blocking) it into a period bonnet is a faster way to make a hat than to sew individual strips of straw plait into a hat. In truth you can use a flat pattern to make cardboard blocks to help with that. Several of my patterns have the instructions for this you can even use it on several I do not mention it in. One thing to keep in mind is that sewn straw hat will compress a bit and stretch a bit but not over an inch or so in girth so what you start with needs to be close to you finished product. The finer (narrower) the straw plait in your hat the less you can reshape it. Choose a 7mm plait over a 5mm plait.