ANP comb or "inserts" are plastic combs with the cells already formed in
the mfg process.  They were advertised as a varroa control system, I think.
The cells are narrower at the top than at the bottom, or something like
that, and this for some reason is supposed to hamper the success of the
mites.
 
Maybe someone else could give us some details?  I'm not sure if the wider
cell bases are supposed to get the bees to feed the brood more food,
resulting in their speedier development (??) which would frustrate the
mite's reproductive timing.  I remember the manufacturer or dealer had a
full back-cover ad in Gleanings for some time.