Try Scotchguard or you can purchase a clear vinyl in some Walmart stores or most larger fabric stores.

Hi Joan,
I didn't forget i owe you an email.I printed it out so i wouldn't forget,hope to get to it this weekend.Hope things are well with you.TTYL
Kathi

Since the cushions have a plywood bottom which will warp if the wood gets wet, I doubt you can totally waterproof the total cushion unless you varnish the plywood to seal the wood. You are better off taking the cushions inside and store them in a convenient dry location so moisture doesn't get into the foam and a mold/mildew farm begins.

You can still cover the set with the plastic to keep it clean if you are in the southern or southwestern states and don't get a lot of snow...there are clear vinyl covers to cover the whole set at discount stores, catalog stores, etc. or the big box and discount stores have clear vinyl drop cloths you can use for a cover. In the northern states, we take the sets inside to store them for the winter, or leave the frames outside covered and take the cushions inside and store them in a dry place.

When you decide it's time to recover them use PVC plywood in place of the plywood. Add the foam and staple the covers on as usual.

Varnishing plywood is only a stopgap measure. It WON'T work for the long run. If you are lucky there will be be holes drilled through the plywood, but that's not generally the case, sadly. If there are holes in the plywood base try turning the seats over and allowing the sun to work its magic.

Short of keeping the rain off the seats entirely, there is NO way to truly "waterproof" anything.

Thank you Chelone.

If you wanted to, you could make new seat covers for the set without the plywood backing, sew a full seat cover since most wrought irons chairs I've seen have a solid seat, and the purpose of the pads is to prevent the imprint of the chair design in one's backside and provide comfort.

I read on a another forum where they covered cushions with
shower curtain material...there are some Cute shower curtains out there.
hope this helps...

When I read that the foam was over plywood and the covers were stapled on I simply assumed the plywood base was cut to shape to sit down in the chair's frame. I suggested the PVC plywood because it is becoming the norm in the marine industry for boat seating that is "built in" to the aft deck or cockpit. We always drill drainage holes in it and use reticulated foam to facilitate drainage.

My own chairs are like those you describe, Stitch., they have a contoured metal "mesh" "deck" and back. I made the cushions for them as you describe, using textilene on the back, Sunbrella on the top, and sculpting the foam to fit the curve of the mesh. They are corded and held in place with strategically placed snap tabs that wrap around the frame of the chair.