Hi plasticpitchfork,
I think you may be paying too much attention to specs that will have no meaning to you in real life. Post #13 here has more about the most important parts of the “value” of a mattress purchase and when you get overinvolved with this type of “theory” and analysis you will end up at the beginning of a learning curve that can take years before you will be ready to buy a mattress only to find it will make little difference anyway.
You can see my thoughts about the importance of knowing whether a mattress is closer to a progressive and differential design in post #2 here. These are only generic descriptions that can be used as to help understand some basic concepts of mattress design but it’s really not important which one a mattress is closest to as long as it’s a good match for you in terms of PPP. One isn’t any “better” than the other.
In a word no … it’s not something that you need to ask about. Many manufacturers may not even know what it is (although some would) and it’s certainly not a spec that would be important to know. It has no relationship to any weak link in a mattress. It’s not the type of information you will need unless you are a mattress designer and even then it would only be one of many other specs that could be part of choosing the materials and components in a mattress design. In many cases a mattress manufacturer will label their polyfoam as HR if the rep from their foam supplier calls it HR … whether it is technically correct or not. You may also see some HD polyfoam that is higher density than some HR polyfoam because not all polyfoam that is more than 2.5 lbs density is HR and you will often see polyfoam that is lower density than 2.5 lbs that is labeled HR (which would be more correctly called high performance or high comfort foam). I would stick to the basics.
I’m not sure where you read this because it’s certainly not the case and I think it can be a very good support layer and can be very durable in higher densities (see the guidelines here).
They are one of the members here yes (the membership list is here). Density, compression modulus, and resilience are part of the technical specifications for HR polyfoam (see page 4 here) but these are used quite loosely in the industry. To be accurately labeled as HR polyfoam it would need to have a 2.5 lb or higher density, a compression modulus (support factor) of 2.4 or higher, and a resliency of 60%. If a polyfoam has all three then it would be technically correct to call it HR.
In the end … most of the information you are “studying” will more likely lead to paralysis by analysis and information overload than it will help you choose a more suitable, a more durable, or better “value” mattress.
Phoenix