My wife set up a sole proprietorship this year and she gets to write off many things. The big one is materials.
This got me thinking.
I get taxed on every puzzle I sell. If I were to have a sole proprietorship for puzzling (even though it is not even remotely profitable for me), could I write off all of my materials from my taxable income?

So, you want to set up a business which loses money so you can write off the losses against your taxes? Good luck with that

I get taxed 25% in federal alone for the puzzles I sell. The way I see it, this is a business.

The prospect of writing off your materials can seem interesting but keep in mind you will probably have to do a lot of accounting which isn't much fun.
I do have the equivalent of a sole proprietorship because it makes a lot of sense for me but there's quite some extra work involved.

I posted here about my puzzle "business". I am not incorporated but do write off my costs, which for some time included a lot of TechShop visits (miles, fuel, membership) and materials cost.
Given how unprofitable I am, this came out as a tax deduction for me, although not overly significant.
I'd encourage you to itemize and deduct what you consider fair. And accountant can help, for example mine helped me by telling me the current per-mile deduction for business related travel.

Dave

If you are declaring each puzzle for tax purposes then yes of course you should claim for materials. I am not sure I understand your current set up though. Why do you get taxed on every puzzle if you're not self employed?