Hi bruby,
The first two numbers are the density of the polyfoam and the second two numbers are the IFD (firmness) of the foam. The “industry standard” is 1.5 lb density (and many manufacturers use lower quality/density than this in some of the foam layers in their mattresses). 2036 means that they are using a 2.0 lb polyfoam which is a good quality and durable material that as he mentioned is higher than the industry standard (which IMO is too low outside of two sided mattresses or lower budget mattresses). The firmness would be 36 IFD which would be a firm foam.
The IFD (firmness) information isn’t important because your own personal testing will tell you whether a mattress is a good “match” for you in terms of PPP (Posture and alignment, Pressure relief, and Personal preferences). The foam quality/density guidelines I would suggest are in post #4 here.
Leggett & Platt is a huge company (bigger than any of the mattress manufacturers) and supplies most of the innersprings that are used in the industry to most of the mattress manufacturers. Of course they also have a huge variety of different innersprings that they supply some of which are more costly and some less costly and each one has different properties but the innerspring in a mattress isn’t generally the weakest link in a mattress anyway because the materials above the spring is where durability is most important because these will generally be the weakest link of a mattress and the first to soften, break down, or sag. There is more about the different types of innersprings in this article and in post #10 here and you can see some general information about the different types and categories of innersprings that are made by Leggett & Platt here.
Phoenix