Bobbinalong

I buy the thin plastic chopping boards, cut to shape and put in a sleeve. Use two layers if they are too bendy.

JanineH

I cut a piece to fit from a worn out cutting mat and made a sleeve for it.

Garden Gnome

I have used things like foam board, but I found the bottom was too rigid and when banged against my leg or someone's back, etc, felt more like a weapon than anything else.
What I finally settled on was a couple layers of the plastic that school folders are made of. Put into a cloth envelope, it works pretty well. And they bend without breaking, which was a problem with cardboard.

ILoveToQuilt

I use a folded up magazine, taped with masking tape to flatten and put inside a fabric envelope. Reduce, reuse, recycle.

KalamaQuilts

old rotary matt for me too

sewingsuz

I have used the cross stitch plastic and made a sleeve to match inside fabric. I have also covered that fabric with clear contact paper so you can just take it out and wipe it off with damp rag.

Mkotch

I have cut up a brown, heavy cardboard box a few times - just make a fabric sleeve and tuck it into the bottom. That makes it removable.

Little Lulu

THANK YOU everyone for your suggestions. I ended up purchasing at Lowe's a piece of acrylic and having it cut. WORKS PERFECTLY. I got 6 pieces out of it so I am so happy. It is strong and thin so it doesn't weigh down the bag.
I would have never thought about it, but when I went to look for laminate sample or ply wood, the young man suggested that. Quilter buds are the BEST!

obie2

Joan Hawley put up a tutorial about supporting the bag bottoms. You will find it at LazyGirlDesigns.com. The product she uses is called Stiff Stuff.

trolleystation

Our neuro surgeon has 'blessed?' us with all of our old outdated xrays I am going to try to use them as bag bottoms.