As mentioned earlier, most of the heat escapes through the cover, not the cabinet – so covers are very important when it comes to keeping in the heat.
Thickness isn’t the main thing that matters. Consider the engineering, materials, attention to detail and workmanship. High quality covers use marine grade vinyl, firmer foam, more robust aluminum rails, stronger stitching, and better handles/clips/locks. Low quality covers fade faster, come apart at the seams sooner, get saturated quicker and the hanging skirts tend to shrink and crack.
Some brands cheap out on their hot tub covers. I suppose it makes sense financially from a business perspective because a cheap hot tub cover costs considerably less than a high-quality one, and most consumers can’t tell the difference by just looking at it.
Potential buyers might ask if it comes with a cover, but they very rarely ask, “How good are your covers?”. And even if they did ask, the salesperson would likely simply say “really good”, and that would be the end of that conversation. So why would a price-conscious brand pay 30% more for better covers if it won’t affect sales?
Some brands brag that their covers are tough enough to walk on, but the truth is that they don’t tend to last much longer than normal covers, and they cost much more to replace. The problem with these covers is that like normal covers, the foam slowly becomes saturated from moisture. That makes them lose their R-Value, and they become super heavy – often sooner than normal covers. So unless you actually plan to use your hot tub as a stage to stand on, those covers don’t make good sense.