Both the standard X-Plus (M4, L4, etc.) and the "Premium" (aka "Air Plus") diapers are cloth-backed, but the Premiums are supposed to be breathable. I found that they get clammy on the outside of the diaper and... er... are atrocious as containing odour...
I think there are one or two retailers in the US that have some kind of special arrangement to get the officially discontinued plastic-backed Abri-Forms, which stay snug against your body (unlike the fake-cloth ones which sag).
If you can still find them, I'd go for plastic-backed. Otherwise, I'd probably switch to a different brand that still has plastic backing.
Hope this helps... :-)
I looked on the XP Medical site and the X-Plus are plastic backed. I'm wearing some M-4's from there now. I ordered a case of M-3's yesterday that I'm going to use to replace my Attends Waistband Style.
They are also plastic backed. I think the cloth backed should be about same as far as performance goes. They'll also be a little cooler when your out and about plus being quieter.