Hi xtrojan626,
Latex and memory foam are very much apples to oranges comparisons and they really don’t have an “equivalent” between them. Memory foam is a slow response material where the firmness varies with heat, humidity, and time while latex is a fast response material where the firmness is consistent in most conditions. There are also different types of memory foams with different types of responses which may feel very firm in some circumstances and very soft in others.
Most fast response foams (such as polyfoam and latex) are rated for firmness softness in ILD or IFD which are reasonably comparable to each other (if the testing uses the same protocol). With memory foam however … ILD is much less meaningful because it will vary with temperature, humidity, speed of compression, and time. Because it is partly viscous as well as elastic … it’s firmness will also depend on how fast you compress it (just like if you “slap” honey it will be firm but if you put your hand into it slowly it will be soft because it will take time to form to your shape).
Having said all that … most memory foam would be considered soft with an ILD range between about 8 to 18 (although as I mentioned it’s not really a meaningful spec with memory foam). ILD with memory foam is more useful to compare one type against another rather than against other materials. Because it is so soft … it isn’t use in support layers of a mattress (you would sink into the mattress too far with your heavier parts) and all memory foam mattresses need some type of firmer support layer underneath the memory foam.
With latex … 24 ILD is usually considered soft (which would be considered to be a very firm memory foam) and ILD’s in the upper teens or even lower teens are considered to be extra soft. It is very rare to find Dunlop latex that has an ILD as low as the upper teens (the softest is usually in the low to mid 20’s but there are a few exceptions) and medium Dunlop would be firmer yet (depending on the ILD that someone was calling medium because Dunlop isn’t consistent in it’s ILD from the top to the bottom of the layer of from end to end or side to side).
Talalay latex tends to come in softer versions than Dunlop. Blended Talalay is available in 19 ILD or 14 ILD which if you were forced to make a comparison would be the closest to memory foam in ILD terms but this would be very misleading and it certainly wouldn’t be “equivalent”.
So overall there really isn’t any comparison between memory foam and latex and even comparisons between different memory foams can be “tricky”. Post #8 here along with post #9 here talk about all the many variables involved in comparing the feel and performance of different types of memory foam. If you were “forced” to make the closest approximation it would probably be the softest versions of blended Talalay or perhaps a Dunlop layer that was legitimately in the upper teens in terms of ILD but again they would still be very different. You can read a little more about the different versions of latex in this article.
One thing that most people would agree on though is that “medium” Dunlop would feel firmer than most versions of memory foam regardless of the type of memory foam you were comparing or the circumstances. The softest possible Dunlop layer would be closer if you wanted to stick with Dunlop (it would probably be in the range of low/mid 20’s).
Phoenix