stuck on material search

[hookinghippie32]

Hello my beautiful crochet Gurus!!! I will introduce myself to you below my question so it doesn't get lost in my ramblings! I'm excited to be here!
I have started a pumpkin basket pattern and the top calls for a piece of cardboard or craft rubber sheet to line it under the stuffing. I want to be able to wash it so cardboard is out. Is rubber sheet the same as those thin foam mats that you can get in a million colors at the craft store? what exactly am I looking for? and how firm does it need to be? I feel like a floppy thin foam mat won't keep the roundness up top instead of in the bottom of the lid but then again I'm still a greenhorn with crochet. thanks!!! ps for reference the pattern I'm following is the pumpkin basket from Ravelry by Hannicraft

My name is Kate and I am a fiber arts enthusiast with a new love for crochet! I first got my hands on a hook years ago when I was in a fiber arts program that mainly focused on weaving but the course required me to try many fiber arts! I had a short assignment with crocheting that sadly left a bad taste in my mouth but did teach me some basic stitches. (I hold stress in my shoulders and locked up my work pretty quickly. Making my 3 tiny samples was a nightmare to complete on time) In 2020 I had just moved to a new city 5 hours from my hometown and had put my crafting in storage in my old town until I got my own place and had space..... lockdown happened only a few weeks after I got settled with friends. I was going crazy and my roommate suggested I get an easy startup craft and I remembered crochet. all I needed was a hook and yarn and I would be set! thank goodness for youtube and time! Now crochet is my therapy and winding down!

I look forward to spending time here!

[Bailey4]

I'd suggest plastic canvas.

[Granny Square]

Looking at the pattern you linked--why does it need lining between the inner and outer layer of crochet?  I would not use the stuff you suggest, it does not hole up well (crumbles).  Plastic canvas is the bee's knees when you need to stiffen something (I could see if the bottom was 2 layers and sewn together, putting the canvas between the layers for a trick-or-treat basket for bottom sturdiness would be ideal), but 'to line under the stuffing' implies a moisture barrier of some sort (?) or that the stuffing might show thru the stitches; the crochet fabric should be tight enough to not require a lining. Is it for stuffing the sides?  I'd skip the lining, make sure your fabric is solid enough so the stuffing doesn't show and stuff it with polyfil that you can find in the craft store. 

I made a somewhat  smaller but similar basket years ago (not quite as realistic looking as yours, had smooth sides and didn't have a lid) and it didn't need, or call for, a lining; it was basically 2 bowls (smaller inside one, bigger outside one) sewn together at the top, with stuffing between.