Hi scott,
I can’t confirm this but i would have my doubts about whether it is 20 ILD based on the feedback. I also believe it is probably blended Dunlop latex (see http://www.classicmattress.com/about_latex_foam.html ). Dunlop also doesn’t have a consistent ILD across the surface. Taking all of this into account … I would think it’s “safer” to assume it’s a little more than 20 ILD (mid 20’s?) and it would also be firmer than Talalay in a simlar ILD. Of course this is just '“educated speculation” and it would be safe to say that it at least is in the “soft dunlop” range of ILD’s even though Dunlop ILD’s are never exact from top to bottom or across the surface of the layer.
It may also be a good idea to check your box spring in case that’s the problem or contributing to the sagging. If you have an OMF model that has thick polyfoam layers on top (pillowtop or eurotop) then a topper may not solve the issue anyway if some of these layers have softened and will just “follow the dips”. Post #4 here has more about this.
This probably has more to do with the type of latex than anything else. Blended Dunlop is the least expensive of all the forms of latex although different outlets will have a range of prices. Walmart is the lowest I’ve seen for this particular topper although others also carry it at low prices and Amazon had it for a similar price but are out of stock. Of course WalMart has a great return policy which can reduce the risk but sometimes it’s at the price of accurate information.
For example this is another blended Dunlop topper for about the same price.
100% natural Dunlop or blended Talalay in the same thickness will generally be more expensive (although not a lot more if you look at some of the choices on the list here). If you add wool or other types of covers it can be even more yet but there are also wide price differences between different manufacturers and outlets which accounts for some of the big price variances as well.
Phoenix