Brian
At an expo i had a polystyrene molder look at the Paradise hives and he commented on how dense the material was. He could tell by the closeness of the mold release marks on the hives
Therefore i am unsure if you will get the same performance out of polyurethane.
Agreed that density is important and the density of the PolyUrethane can be achieved by putting the forming mold under pressure.
There are a lot of beekeepers in The UK making PU hives and they are very strong.
Here is a link to a video
https://www.youtube.com/watch?v=NvO0B_zsZ_8 I removed my headset after about an hour of watching videos. because couldn't understand Russian. But did learn a lot by translating the comments.
Here is the spec sheet of the PU product used in Russia.
Chemtrast SKD-50
Production of mounting graters, beehives, decorative finishing and structural elements of furniture, headboards for beds, cornices, ceiling sockets, linings, mascarons, etc.
Component A: Chemtrast KAD-50 (packaging: 200 kg, 50 m3 kg.)
Component B: (packaging: 250 kg, 55 * kg.)
Start time
20-30 sec
Foaming density
50-65 kg/m3
Product density
80-120
Parameter Meaning
Start time 20-30 sec.
Gelling time 55-170 sec.
Apparent density with free foaming 50-65 kg/m3
Product density 80-120 kg/m3
Surface hardness 20-25 Shore D
Tensile strength 30-40kg/cm2
Elongation at break 7-8%
Compressive strength 0,5-0,8 N/mm