Hi church11,
For some reason … comparing latex to memory foam in terms of ILD / IFDhas been a popular question on the forum over the last few days.
ILD / IFD @ 25% is really only one measure of a foam’s softness and by itself is best for comparing the same types of foam. Other measures include IFD at different percentages of compression and compression modulus (which measures the ratio between 65% compression and 25% compression or how quickly a foam gets firmer with deeper compression which may be an even more important a “softness” measure in many cases than ILD / IFD). Even using 25% ILD to compare latex to polyfoam or Talalay latex to Dunlop latex can be misleading (see post #6 here) partly because of their different compression modulus but partly as well because of the different methods of testing IFD between different materials and even in different areas of the world.
With memory foam … IFD is really a meaningless number (except perhaps as a rough comparison between memory foams) because the method of measuring IFD is not really suitable or meaningful for memory foam (see under “resolving testing procedures” here) and because IFD with memory foam can change in response to temperature, humidity, and the length of time the memory foam is compressed. The firmness of a memory foam layer will also depend on its response time and temperature sensitivity as well as its thickness. You can see more of my replies about the comparison (and another manufacturers guess about how their memory foam may subjectively compare to latex) in post #2 here along with post #2 here. Overall … IFD comparisons between different foams and especially between memory foam and other types of foam is a very subjective and not particularly accurate or meaningful exercise.
Phoenix