> There is a need for an environmentally friendly bee hive insulating
material.

I ran into this issue a few years ago, and bought some obscure stuff that
has been around since the 1980s, but is now more of a commodity - "Icynene".

I think it could be used, but it is a complex beastie as compared to the
straightforward Polyurethane.

It's made from castor oil (no petrochemicals), but it has a few drawbacks,
such as being "open-celled" so no air is trapped, so it can become soaked
and water-logged if exposed.  But the airflow is ventilation, which might
help in a beehive, as the insulation would provide its own vent.  Because of
the lack of air-trapping, it runs about HALF the R-Value of the polyurethane
foam for the same thickness.  It can be either sprayed or poured. Because it
can be poured, the liquid gets into even tiny cracks, and leaves no voids. I
used it to insulate my uninsulated wood-frame residence in very damp Jamacia
in 2017. Spraying would have required too many access holes to be
cut/drilled, pouring made it far easier, as a liquid seeks its own level at
all points in a cavity, and this was a DYI project.

On the plus side, it is flexible, so it will stretch and bend as wood
trusses and studs expand and contract (or bend slightly in hurricane winds).
On the minus side, you need to know your cavity volumes VERY well, as this
stuff expands much more than poly does, and it could easily start popping
drywall off your stud walls if you forget to carry the 2.  Best to take it
in stages.  A $10 cellphone borescope is a handy tool as it lets you see how
much the "cake" has risen inside any one stud wall.  Also on the minus side
- did I mention that it is OPEN CELL?  You need a vapor barrier for
human-occupied structures.  My place has a vapor barrier, the idiot who
built it decades ago decided that he did not need insulation, soundproofing,
or any of that stuff.  Or maybe he got scammed by the contractor - we'll
never know.

Polyurethane foam does comes in some "green" versions, made partly from soy,
but still using mostly petroleum.

And give the alleged "biodegradable" plastics a wide berth - breaking down
those long-chain polymers into shorter chains is a way to create
microplastics, which turns a simple plastic bag one could pick up into an
ecological cluster-bomb, leaving uncountable numbers of tiny bits of plastic
shrapnel all over the landscape and the seas.

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