There is a product on the market called a"Wall O' Water"

There is a product on the market called a"Wall O' Water".  It is adoubly thick cylinder made of polyethylene which is often colored green, blue,or red.  This cylinder is about 1 foot indiameter and has cells that are filled with water. The directionssay to fill the cells with water and set it out in the garden before the lastfrost; after about 4 days, you can plant frost sensitive plants withoutworrying about them freezing to death. Do these things work or are they a “joke” equivalent to “DehydratedWater”. What are the physical principles behind how they mightwork?  (Hint: there are boththermodynamic and light absorption considerations.