Insulation for a steel urn ?

Your question has two disparate parts and the first one is muddled.

Do you want to insulate a steel urn to hold boiling hot water - which means the temperature is limited to 212F/100C - or for boiling the water on a heat source, which means the much higher flame or burner heated gases will be striking the lower parts of the urn.

Since you don't want the material to absorb (much) water, spray on insulating foam would be a good choice for the former while almost nothing is good for the latter unless you use silicone rubber which stands high temps but is pretty bad as an insulator.

As for waist coat and hat, this is such a different area, you need to post it separately and probably in Games & Recreation/Hobbies & Crafts where sewing and costumes show up a lot.

Usually a good ceramic coating was used for this purpose, such as the Le Creuset cooking pots. I am thinking the iron pots were dipped into a liquid ceramic mixture and then kiln-cured. That would be a good thing to look up on "How It Was Made" for video for ideas.