Hi Martina,
The specs and pages on the site about mattress layering and design are generic guidelines that can be useful as a basic starting point or to help with understanding some of the concepts behind different mattress designs but there are too many variables to use specs as a way to choose a specific mattress based on theory at a distance (see post #2 here). Only your own testing or personal experience on a mattress can tell if the mattress is “right” for you. With an online purchase your more detailed conversations can help you choose the mattress that has the best odds of success based on the “averages” of their customers and any other information about your preferences you are able to provide.
I’m not sure where you read this but durability is relative to each person and also on the type of materials in the mattress (although softness is one of the durability factors). You can read more about the factors that affect durability and the useful life of a mattress in post #4 here.
I leave value comparisons up to each member to decide for themselves because each person may have a different idea of which parts of a mattress or topper purchase are most important to them. Of course I would make sure that you are making apples to apples comparisons in terms of the thickness and type of latex (type and blend of the latex) and the other factors that may also be an important part of value to you (such as the cover, shipping, return policies, advice etc).
All Talalay Latex made by Latex International has been certified by the same OekoTex standard 100 criteria including both the blended Talalay and the 100% natural Talalay. They use the blended Talalay in their mattresses and toppers. They don’t use a spray to make latex fire retardant and they will provide you with the details of the fire retardant that is used in any of their mattresses if you ask them.
There are different grades of latex that may make a difference in overall consistency and appearance but in general if the type and blend of the latex is the same then they would be equivalent in terms of performance. The pieces that are part of different sizes can be glued together by either Latex International or by a separate fabricator but it would mostly be by LI.
This is a question that should be part of your discussions with each manufacturer because they know more about the specifics of their mattresses and the type of customers that tend to do best with each of their options “on average” than anyone else.
All foam materials including latex will become softer over time but this process is slower with latex than with other foams. The softness of latex (or any material) is also a factor in its durability and softer will tend to be less durable than firmer layers but this also depends on all the other factors that are involved in durability that are in the post I linked earlier.
You really can’t unless you have specialized equipment that tests ILD and for that you would also need a 6" layer of latex (the thickness of the layer affects the test because ILD is usually measured at 25% compresssion). If there is still a tag on the layer then it may have the ILD measurements for the original 6" core but this may not be on a layer you receive because the core that is tested is cut into thinner layers that may not include the tag.
Phoenix