What do you use to stiffen the bottom of a tote/purse?
 

I am about to make a tote bag for my DD and a purse for an upcoming trip for myself. My question is -- what does everyone use to create a flat, nonbending bottom on their bags? I don't want to put all the work into piecing a nice bag and have it droop.

In the past I have used plastic needlepoint canvas. I've always liked it because you can cut it very precisely to any size, but it is not quite as stiff as I would like. Any ideas?

Many thanks to anyone who cares to share.

What about doubling the plastic canvas ?

I sewed two pieces together with the top one being larger to make a D. This works great.
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I made My Dog Lilys Bag and wanted it Stiff too! I used some Plastic Binders I found at Goodwill, Not the ones with cardboard inside them But the ones Made of Solid Translusent plastic. :) PS: to Cut it I used a Xsacto knife

I make a fabric sleeve and insert a piece of foam core board and then sew it shut. It fits great in the corners and can be removed if you need to wash it. I've also used the plastic canvas.

I like nans suggestion. you can also use a piece of plastic. like a ruler maybe. I would do like ksdot says and make a sleeve for it that you can take it out of. the bag so it can be washed.

I recycle lids from old plastic packing crates. It cuts easily with my old rotary cutter and is machine washable. Very stiff, no sag and lasts longer than the fabric.

I use foam core board. I round off the corners a bit so you don't have that sharp point wearing on the fabric.

I use self stick floor tiles two put together. Cover with a sleeve that matches the inside of the bag.

I had the DH to cut a piece of acrylic and put it inside a removable "sleeve"....this way you can remove the acrylic and toss the rest in the wash as needed.