Question:
would still put it in a sealed poly bag for good measure and inside the
vinyl cover.
What are the downsides in using it for this application?
Answer:
None that I know of. Chemically, it is the same material. Extruded is more
rigid and will probably hold up better for your use. If better fused EPS (expanded beads) can be made, it sure doesn't seem to be
available. So hot tub cover makers all continue to use the regular stuff. To
help overcome water logging, they all wrap their EPS cores in sealed 3 or 6
mil poly bags. These are then encased in heavy vinyl covers.
However over time these inevidibly leak, waterlogging starts, and the cover
quickly becomes as heavy as lead and cracks.
