Thanks, JD, for the info-- Yes, we're hoping to retain the water's daytime heat as we have a pump, but no heater-- One of our renters last winter remarked on the chilly water so we thought we'd look into it-- The website solarcovers.com has pre-cut clear plastic covers for around $200-- As you said, I'm sure they won't last too long! I like your idea of having the roll-up device made in the DR-- Thank you again!!
The only stuff that really ADDS some heat, is a bubble sheet material. It has a better insulation factor and the translucent plastic bubbles act somewhat like little lenses with the sun rays.
Now, with your tenants: I would NOT do it at all.
First of all, floating flexible pool cover can be a life threatening trap to children, pets and drunks, as if one falls incidentally or for "play" onto such a cover, the cover WILL wrap itself around that body and pull it down, most inevitably drowning the victim(s).
Secondly, it's a somewhat delicate item and if it's not handled with a lot of care, it won't last.
I'd rather suggest adding some solar heating by simply using a small low consumption circulation pump and a good mess of black irrigation pipe facing the sun.
It will not turn your pool into a boiling jacuzzi but still yank the temperature up a couple of degrees (C) to make the pool nice year 'round.
... J-D.