bees eating plastic?? Higher density, harder, polystyrene.
I run cedar 14x12 (12 this year), a polyhive with an extension piece underneath to make the brood box 14x12, and at a different apiary I use Poly Langstroths [six] ... Swienty version. The Poly hive is ok, though flat-packed. The Swienty Langstroth boxes are one piece - brilliant!
Having started [and still using] with long lugs on 14x12, and , I find the short lugs easier ... never thought that would be the case, but they are!
I use standard Langstroth boxes throughout - no smaller "supers" ... and , yes , a couple of storming colonies make the one box seem a bit small, especially when I compare then with the 14x12. But, hey, small price to pay, and uniformity of box size is a boon.
Yes, Poly's are a LOT warmer, with a looser winter cluster and earlier build up - and yes, they don't avoid the cold walls .. 'cos they ain't cold!
And cost!!! Poly Langstroths are widely used in Europe, and they are LOADS cheaper than the smaller-market-UK-only PolyHive [Nat]. Carriage is by volume, rather than weight, so flat pack Poly's [e.g somePolish and German varieties] ... are cheaper to import ... but I curb my impatience and get Swienty to bring mine to Stoneleigh, from where i collect then carriage free!
On the subject of Poly Langstroths ... Swienty ones have flat tops to the wals of the boxes ... a couple of others [e.g the excellent and cheap ones sold by Modern Beekeeping] are rebated ... much like you see on those excellent German IWF videos ... but as I like fiddling about making apiguard ekes, clearer boards etc, I get on better with the simpler flat top approach.