7FT x 7FT Hot Tub Heat Retention Blanket for Hot Tubs Geo-Bubble Gold/Jade 500 Micron. The Geo-Bubble design & construction offers the most durable thermal blanket available. 3 ways the 7FT x 7FT Hot Tub Heat Retention Blanket Gold/Jade 500 Micron can save you some money: 1. This cover reduces the evaporation of water by 95% 2. It will save you electricity due to heat retention. 3. It protects your spa covers from the chemicals (foaming) in the spa water, extending the life of your top cover. The Heat Retention Blanket is very easy to trim into shape with some sharp scissors Please be aware that your blanket may have a join as the material is cut from a 2 metre roll.