What Spa Cover Thickness Should I Order?
While ordering a new hot tub cover should be easy, it can be confusing with all the different thicknesses available and the best type to order for your new replacement hot tub cover. Here is a quick guide on different foam thicknesses.
4" x 2" 
If you purchased your hot tub, you most likely received what we call an OEM factory-produced cover. These covers are usually of lower quality and minimum foam thickness to provide a spa cover for your new hot tub. These covers generally have a foam thickness of 3 inches, tapering down to 2 inches, while some will also come 4 inches to 2.5", considered an indoor hot tub cover. While it can still be used outdoors, it provides minimum thermal efficiency and does not last as long as thicker foam covers. So, these covers should only be ordered if you have a smaller hot tub placed indoors.
4" X 3" 
Higher-end hot tubs that are larger and placed outdoors typically come with a foam thickness of 4 inches, tapering down to 3 inches. This is the starting point for a hot tub cover that has a quality thermal rating and will give you an adequate life expectancy. Also, always ensure the foam is rated at 1.5 lbs density, which will support light snow and weight on the cover. Some suppliers to lower the price of a replacement cover will produce the foam with 1 lb foam. While it will still keep heat in your hot tub, it is limited in what it can support, especially if it is larger.
5" x 3" 
So, if you want to upgrade your replacement hot tub cover to something better than what you received when you purchased your hot tub, a 5" x 3" foam thickness with 1.5 lbs foam density is a great starting point. This cover increases the thermal efficiency of a cover by 20 % compared to a 3'x2" cover and is strong enough for most applications. Standard-rated R22, the extra cost to purchase this thicker cover usually pays for itself in the first year, and these covers easily last 5-7 years if maintained properly. Suitable for all climates and seasons and not too thick to handle manually or with a cover lifter.
6" x 4" 
The thickest foam you can purchase for a replacement hot tub cover is 6" tapered down to 4". Where would you order this for? These covers are usually ordered with a 2 lbs foam density and are considered walk-ons. Small animals and snow loads up to 200 lbs can stand on the cover without breaking the foam. If your hot tub is larger than 90", sunken in a deck, or at a location such as a vacation property, and snow will accumulate, then these are the perfect solution for a replacement cover.
So there isn't anything like a bad hot tub cover; there are good, better, and best thickness and quality depending on your application. Spending a little more does get you a longer life expectancy and thermal efficiency, reducing the operating costs of your hot tub.