"What is the R-value of your cover"? While this is the most common question asked when comparing covers, the answer can be the most deceptive. The following, though rather lengthy, explains insulation and R-value. The short answer to the R-value of our covers though is:
The Deluxe spa covers with standard 1.5 pound density foam cores, have a minimum insulation value of R-14, the Extreme spa covers with the standard 1 pound density foam cores have a minimum insulation value of R-21
The insulating core of almost all spa covers is EPS (Expanded Polystyrene). The insulating value of this product is very specific, and is listed in the table below. Please note, the R-value shown is for 1 inch of thickness.
Remember, all EPS foam of equal density has the same R-value!
R-value describes a material's resistance to the flow of heat. The higher the R-value, the slower heat will travel or conduct through a material. Better insulating materials tend to have better R-values.
Heat flows by three mechanisms: conduction, convection, and radiation;
Conduction is the molecule-to-molecule transfer of kinetic energy (one molecule becomes energized and, in turn, energizes adjacent molecules). A cast-iron skillet handle heats up because of conduction through the metal.
Convection is the transfer of heat by physically moving the molecules from one place to another. Hot air rises; heated water thermosiphons; forced-air heating systems work by moving hot air from one place to another.
Radiation is the transfer of heat through space via electromagnetic waves (radiant energy). A campfire can warm you even if there is wind between you and the fire, because radiation is not affected by air.
R-values by definition, only measures an insulation's ability to resist heat loss by CONDUCTION.
The above's relationship to spas is this; heat from the spa water rises by convection and radiation. As it rises it heats the underside of the cover, then moves through the cover by conduction. Increasing the covers R-value reduces, or slows the rate of conduction. There are also two ways to reduce the rate of convection, the first being a floating blanket, the second being our optional exclusive Reflex Energy Shield used for the covers underside material.
R-value is a term coined by the FTC in response to a need for a way to compare the relative effectiveness of various forms of insulation. R-values are measured by testing laboratories (ASTM), usually in something called a guarded hot box. As air within the test hot box is heated, convection takes place, causing the heat to rise. As the heat rises it warms the underside of the foam where upon conduction of the heat through the foam begins. The R-value is the ability of the foam (or other material being tested) to slow this conduction. Heat flow through the foam is calculated by keeping one side of the material at a constant temperature, say 90°F (32°C), and measuring how much supplemental energy is required to keep the other side of the material at a different constant temperature, say 50°F (10°.C)--
Various industries are required to have their products R-value tested by ASTM under very exact testing perimeters. One of the parameters of this test is the temperature at which guarded hot box is heated to, AND the temperature the other side of the test material is kept at. Changing either of these temperatures will result in different R-value results. Once again, certain industries are required to use ASTM testing procedure and parameters. For these industries, when they list their products R-value (such as R-20) it's understood that the difference in temperatures of the testing procedure is 40 degrees (or R-20 @ 40º). It's also acceptable to list another R-value AS LONG as the temperature difference is listed ALSO (i.e. R-40 @ 20º). Here's the relationship to spa covers. SPA COVERS ARE NOT IN AN INDUSTRY REQUIRED TO HAVE R-VALUES TESTED ACCORDING TO ASTM STANDARDS! When comparing the R-value of a hot tub or spa covers it's important to ask what temperature difference the R-value was calculated at. Our covers are R-14 @ 40º.