This inflatable cover, or bladder, is made of white PVC and goes between the water and the cover of your spa. It provides a sealed pocket of air for insulation. 

Inflate the cover and put it on the water (under the cover), and it will help your water retain heat by adding an extra layer of insulation in the spa. It also decreases sagging of the cover, so the rainwater can run off. If you find the rain water still pools on your cover you can try two things; just before you take the cover off your pool, try tightening the buckles. You can also velcro an appropriately sized ball or swim ring to the underside, centre of your cover to provide a greater pitch so the water runs off. 

Please note that the warning on the bladder should read, stop inflating before the wrinkles disappear. The hot water of the spa pool together with sunlight will cause the air in the bladder to expand. When you take the bladder off the spa pool, if your hand doesn't easily push into the bladder, it is over-inflated. Let some air out. If you leave your bladder over inflated, in due course its shape will either change to the "flying saucer" effect or it will start to leak air. 

Dimensions (inflated)
Length: 160 cm
Width: 160 cm
Thickness: 29 cm

Part numbers
MSpa: B9301079, B9301779

SS23 EU F-OS063W/F-TR062W Spa Shape 6-person Bladder, 1.6M