Took apart my (great quality btw) foam order all natural latex mattress today. Im going in to swap the middle layer (n31) for slightly softer (like N27). Each piece has a label "arpico foam" on it.

 

http://www.arpico.com/rubber.html

 

Looks to be a good quality manufacturer.

 

Also, anybody know why my lowest layer is labeled N90? That seems ultra stiff, but it has a separate "weight rating" (each layer does actually) of 40.4. In contrast my middle layer has a "weight" of 37 and a rating of N31.

 

Im beginning to think the "N" numbers actually mean nothing, and that it really only matters on the foam "weight". Any opinions here?