Hi Manimal,
This is my understanding as well.
The use of fillers in each manufacturers latex compounding formulae is a very complex subject and is really more in the realm of a materials scientist with a PHD degree and years of experience (which I’m not). There are different types of fillers and each of them, along with the quantity used can have such a different effect on both the performance and durability of latex that there aren’t really any simple or generic answers that would be particularly meaningful. In very general terms fillers can be used to increase the firmness of latex, change the properties or change the “feel” of the latex, add fire retardancy, or lower the cost of manufacturing the latex. Past a certain point … the use of “too much” filler can certainly have a negative effect on durability.
Having said that … I would also keep in mind that all latex is a high quality and durable material relative to other types of foam so outside of defective materials or quality control issues you are really comparing differences between high quality and durable materials.
As you mentioned … the use of fillers wouldn’t be an issue with 100% natural molded Dunlop made by the well known manufacturers (such as Latex Green, Arpico, CoCo latex etc) and it also wouldn’t be an issue with any of the Dunlop latex made with the Continuous pour method. The latex where the use of any “hidden” fillers may play a more significant role in durability would generally be with blended molded Dunlop made by some manufacturers and this is the type/blend of latex where I would want to know that there are either no fillers or minimal fillers used in the formula. This may not always be possible to find out because latex compounding formulae in general are closely guarded secrets.
In the case of Latex International … fillers are used at a level that doesn’t diminish product performance over the life of the mattress, but does help reduce production costs. The theory is that it doesn’t make sense to produce a product at a much higher cost that doesn’t greatly outperform the product at a lower cost. In other words … it would have “some effect” on durability but this would be over longer periods of time. At their best … and excluding any quality control issues that may affect the durability of the latex … I would say that in “real life” terms the durability of LI Talalay and Radium Talalay would be very comparable over the length of time that most people would keep their mattress.
You are certainly looking at some good quality/value options and there is more about the most important parts of the “value” of a mattress purchase in post #13 here that may help you make more meaningful comparisons between them.
Phoenix