Hi all. I want to build a split king setup w/twinXLs on adjustable bases. Is there any downside in stacking three individually covered 3" layers versus having them encased in one 9" mattress cover? I’m thinking that the individual wrapping will assist in rotating/flipping layers and also promote a more pillow-top like feel on top. Any drawbacks, especially with the adjustable bases? Thank you!
Hi geo_man,
Welcome to our Mattress Forum! 
Stacking three individually covered 3" layers will act a bit more independently than a 9" layer enclosed in a zipped cover. Independent layers are more likely to shift position when you change the base positioning so you may need some layer readjusting over time. Having all foam layers enclosed in a good quality 9" tight-fitting zipper cover wouldn’t generally have shifting issues as the foams are quite sticky and their weight, density, and enclosure will prevent it.
While having an individually wrapped 3" atop of the existing 6" layers may create a “pillow top feel” to a certain extent, having all the layers in a zipped cover can equally “assist in rotating/flipping layer”. Individually wrapped layers may provide a little more extra protection against foam tearing while handling the layers. Generally, if layers are handled with care this should not be a big issue.
You might want to find out the likelihood of having a wide gap between your bases. Will you need a crack filler of some sort to fill any gap that may exist between units? Do the units have some sort of sync ability or sync cable that allows the two units to work in unison if desired?
Here are some things I’d also keep in mind. when shopping for adjustable basis
Product Quality
• Built quality, parts quality, and features that meet your specific criteria
• Replacement Parts (Long-Term availability if needed)
• Product made in The USA by American Workers with US parts
Manufacturing company
• Long-Term reputation of the manufacturing company (e.g. Leggett & Platt has been in business for over 130 years as opposed to bases made in China and assembled into the US)
• Long-lasting strategic positioning of the manufacturing company (viable business model) that can withstand ebbs and flows of Geo-Economic crisis (e.g. by providing a diverse array of products should the demand for power basis diminish)
I don’t know how advanced you are with your DIY built but you may want to have a quick look at this article by Richmond Bedding expert in adjustable beds to bring some awareness of deceptive online advertising and practices.
Phoenix
Thank you Phoenix for the great info!