Hi Clawdia,
Latex ILD’s are never exact but the difference between 21 and 23 wouldn’t be noticeable but most people would notice a difference between 21 (which would generally be considered to be soft) and 28 (which would be more in a medium range).
Natural or “botanical” latex (same meaning) is latex where the raw materials are the latex “milk” that comes from the rubber tree that is then made into a foam using either the Dunlop or the Talalay method. Synthetic latex is made from a copolymer of Styrene and Butadiene. A blend would use a combination of both in some proportion. Latex International makes blended Talalay and 100% natural Talalay so their 100% natural would also be “botanical” meaning that other than the chemicals and compounds that are used to turn it into a foam … that it only includes the raw latex used to make it that comes from the rubber tree. There is more about the different types and blends of latex in post #6 here.
The active fusion would be very similar to a blended Talalay latex in the same ILD but some people have commented that it feels a little “stiffer”. The 100% natural from LI would be a little less pressure relieving, a little more “supportive” and a little less durable (at least in softer ILD’s) than their blend. Both 100% natural and blended Talalay come in a wide range of firmness levels. They were making toppers with three materials (active fusion fast and slow response, and 100% natural Talalay) but of course they aren’t making the active fusion slow response any longer.
Phoenix