Hi Turtlebed,
Most consumers don’t realize that like any natural material natural latex will have some imperfections, tears, and discoloration and when they first see a latex layer they often think that something is wrong with it or that it’s been used so as I mentioned in the post I linked in the previous reply … encasing the latex in a thin cover would certainly reduce customer complaints from consumers that don’t realize what natural latex looks like and this can be one of the reasons that it’s used.
There are also many consumers that buy a component latex mattress and need to rearrange or exchange the layers until they have the design that works best for them so some people end up handling the latex a fair bit at first. Latex can tear very easily if you tug or pull on it.
Most component zip covers fit quite tightly and they “squish” the latex when they are zipped up. Many people that are assembling a component latex mattress for the first time are convinced that the layers won’t fit into the cover before they zip it up so a small variance isn’t likely to make a difference but you can always check with the manufacturer of a cover you are considering to make sure that it would be fine.
It’s actually fairly simple. You can see some instructions here for compressing your own layers if the size of the layer you have doesn’t fold up and fit into a box that’s small enough to ship by courier.
Phoenix