Foam density represents the strength and R-value or insulating factors of the covers. The denser or thicker the foam the stronger it is which increases the weight baring capacity of the spa cover. It also increases the Insulating properties.
The general rule is this. For every .5 lb increased in density the spa cover's R-Value increases by 5 and the weight baring capacity is increased by about 20 lbs. On this same note for every inch of thickness you go up the r-value goes up 5 and the weight baring capacity is increased by 40 lbs.
Example: if you ordered a 4x2.5 1 lb. cover it would have an R-value of 15 and a weight baring capacity of 40 lbs. If you take this same cover and use 2 lb. inserts instead, the cover would have an r-value of 25 and a weight baring capacity of 80 lbs. To summarize this, all of our covers are manufactured the exact same way, the only difference is the type of inserts we use for the cover. If you are in colder climates or heavy snow climates, the thicker and denser the cover the better for maximum (snow load) support and energy savings. If you live in Florida you won't need a 7x4 spa cover and if you live in Minnesota you don't want to order a 4x2 cover. If you are in a cold weather environment, we usually recommend at least the 5x3 cover in 1.5 lb or better. The thinner spa covers and less dense covers are more suited for hotter less volatile climates. As always if you have any questions or need any assistance in making the right choice give us a call or Contact Us.