To make it clear:
This is definitely unwanted.
By such an application of plastic around the complete winding package, the thermal resistance is only worsened and can be worse in water than without anything in air.
Also this is formulated very euphemistic:
"Outstanding Thermal Conductivity: our filled epoxy materials excel at transporting and dissipating heat from motors and other coil windings, a reduction in core temperature is always achieved."
Only if you compare it to conventional epoxy, maybe. I have found little evidence, that epoxy or other plastics could be enhanced significantly by mixing with copper or silver dust. The thermal capacity rises and conductivity as well, but it is still magnitudes less than the metall itself would have. Epoxy has 0.2 W/mK, pure copper around 400. So if someone tells that the conductivity is 70% or 300% better than epoxy it is still very very bad. Arctic Silver Epoxy is sold for terrific price and they do not even tell you what the thermal conductivity is.
I had frustrating results with this motor design:
I filled the epoxy with masses of copperdust and the windings were burnt after short time. Additionally i closed the bell to have less hydrodynamical losses, i suspect the water was cooking inside the bell.
Lessons learned: 1. Do not care about the hydrodynamical losses, keep the water going through and 2. keep the epoxy as thin and as large area as possible, use very thin epoxy with long curing time and vacuum and let the epoxy dripp off before it is geling too much.
The hydrodynamic power loss you can easily estimate. Measure the no load current in air before and in water afterwards without a propeller. My motor spins with 5700RPM, which is not very much. I think it added 90W to the no load losses, could be slightly more with the slots left open. Water has low viscosity, motor oil has 3 times higher viscosity.
If you plan very high RPM, the losses will be higher, i cannot tell you how much.
From my last motor i have no pictures, sorry, it was built in a hurry and since then not disassembled. It is working fine so far after several hours testing in the sea.
The magnets in the rotor should be covered with epoxy, i had it done in my lathe. Fix a tightening rubber ring inside the bell where the magnets end. Fix a disc with a center hole to apply the epoxy. Use 40 minutes curing time or even less.
Use more tape than suggested by this foto to fix the disc. The disc is made from a solderwire bobbin.
Let it spin for some hours and warm it only slightly, otherwise the tape looses contact and whooosh…you have a decorative memory on walls, clothes, lights.
After curing warm it some hours in an oven at 70°C.
Be careful when lathing the abandon epoxy not to hit the magnets surface.
Be careful when clamping, my lathe has very bad tolerances when clamping the drive shaft, it is better to clamp the bell at the aluminum head directly.