For quick and dirty dipoles I've been using bits of plastic such as old film containers and bits from the kitchen but they're not very strong and not good under strain.
There's a purveyor of plastics near by and I dropped in looking for small squares of perspex(tm) that would suit my application. I was amazed to see that they had a wall display full of suitable squares:
Of course they are samples that are given out to architects. The lady was a little puzzled when I asked how much they are, I got the impression she'd have given me a few for free but asked for a few dollars for ten.
Here's what I made:
And here's the back:
I clearly need to learn how to drill straight and proper strain relief for the dipole wires but this is perfect for my "quickie" temporary antennas.