The method of construction I use for all of my costume heads has been to use a clay positive mold from which a fiberglass head shape is created.

MAIN ADVANTAGES:

1) Refinability:

The use of a clay positive provides a sort of WYSIWYG method of making the form upon which the fur will be attached. You can actually place a piece of fur over the clay to get a general idea of how much the fur will ‘grow’ the overall shape, and then modify it as needed before making the fiberglass head.

2) Late-stage Refinability:

If for some reason you still have a problem... even a major one, the use of fiberglass as a construction medium is very forgiving. The casting can be cut, and re-pieced together to fix defects.

3. 3)Durability:
   

A fursuit head made with fiberglass will last without the degradation that comes with foam.

4) Rigidity for Animatronics:

If you wish to have a moving jaw, and want the jaw to work really well, having a rigid structure is a near necessity.

5. 5)A nice “Compromise” between carved foam and cast foam:
   

If you want to make a head from a sculpture, but doing it in volume is not desired, fiberglass is a reasonable alternative, and the need to make a negative mold from the positive sculpture is eliminated. A clay sculpture in model clay can produce a few fiberglass castings if care is taken in the release process.

MAIN DISADVANTAGES:

1. 1)The MESS!  Fiberglass is messy stuff to work with! :P
   

2. 2)A life cast is a near requirement for close-fitting heads.
   

3. 3)The rigidity makes for more difficulty in storage-- fiberglass doesn’t “squish”.
   

4. 4)Some tools are necessary to cut and shape fiberglass after it is cast.
   

...and the big one...

5) Care must be taken to make the head strong and yet light weight.