I have started to use a piece of foam core board (you get it at the craft store - it has paper on the front and back and a "foam" in the middle) in the bottom of my bags (I make lots of bags). I put this under the plastic canvas piece that I have enclosed in matching fabric. Seems to work quite nicely for me.
My husband buys the scrapes of thin plexi glass from Lowes or Home Depot and uses a cutter and dremel to smooth out the edges. I use those in the bottom of my quilted purses. I cover them with a fabric sleeve and it works great. Hug & Stitches, Liz
Thank you Liz I never thought of asking Lowes for the scraps. I have to go tomorrow for a water regulator for my 5th Wheel so I will check into it.
Rhoda
Recycle pet food Bags could be used.
They make water proof sturdy shopping totes from them.
From Bev
Bev, Thank you already have been using the dog bags for under the puppy pads I use with quilted material.
Rhoda
If you are asking about just reinforcing the bottom of the bag for heavier items, I cover a piece of plastic canvas (that is usually used with yarn) cut to size and it has worked out very well.
For substantial bags, I prefer, twill, denim, canvas, or any fabric designated as outdoor fabric.
Just the bottom of the bag is what I was looking for. Thank you. The bottoms that come in the bag is not strong. Do you cover your plastic canvas?