Hi jbrennan,
ILD is just one measure of the softness or firmness of a foam layer and is a “comfort spec” and not a “quality spec” and is just one of the specs that affects how soft or firm a specific material or layer in a mattress feels by itself. When you are testing a mattress locally then the ILD of the layers isn’t important to know because with careful testing your body will tell you much more about whether a mattress “as a whole” is a suitable “match” for you in terms of PPP than the ILD of the individual layers and ILD itself is also only one of several factors or “specs” that will determine how soft or firm a layer or a mattress will feel to different people and can sometimes be more misleading than helpful (see post #4 here).
The specs you would need to know that would have the biggest effect on the durability and useful life of a mattress are listed in this article.
If you are considering an online purchase where you can’t test the mattress in person then the most reliable source of guidance is always a more detailed phone conversation with a knowledgeable and experienced retailer or manufacturer that has your best interests at heart and who can help “talk you through” the specific options they have available based on the information you provide them, any local testing you have done, and the “averages” of other customers that are similar to you. They will know more about “matching” their specific mattress designs to different body types, sleeping positions, and preferences than anyone else.
Latex is the most durable of all the foam materials (latex foam, polyfoam, memory foam) so an all latex mattress (that didn’t contain any other types of foam) would certainly make a durable choice.
Phoenix