On Sun, 23 Nov 2008 08:14:26 -0500, wrote:

On Sat, 22 Nov 2008 20:03:36 -0800, "Bob F"
wrote:

I suspect that most of the water comes from the spa. A vapor proof layer between
the spa and the cover might make a huge difference, if anyone wants to try an
experiment.

There is a vapor proof layer already, Bob. The foam blocks in covers
are wrapped with a layer of poly. That poly breaks down over time and
then the foam starts to retain water. Some manufacturers use better
poly and heat seal it, while others just use a sheet of poly to wrap
it like a christmas present and hold it together with masking tape.
Beyond that, I discovered that some manufactures have an option for
double wrapping the foam with two layers of poly. It's not an
expensive option and it results in a cover that lasts a LOT longer.

The poly breakdown happens faster if the cover is exposed to intense
sunlight all day long (as was the case with our hot tub, located on
the south side of the house). The new covers have not only the double
wrapping, but also a sloped shape to the poly to get the water to run
off faster, which also should help the cover last longer.