My heads are built on a baseball cap. Being built on a baseball cap means they are easily adjustable not only to head size but where they sit on your head allowing you place the face lower or higher based on your comfort and range of vision. You can also easily adjust the fit with a bit of foam, in the case of the image above I needed that little sliver of green foam sheet to make the jaw sit right since it was a tad too tight, amazing how such a thin little thing made the fit go from "meh" to "perfect" Now if the jaw were too loose I would have put the foam on the back of the jaw.
With my custom carved foam heads the jaw is hinged via tube and rod and works by bumping your chin. The movement is flawless for silent movement but does voice sync decently as your chin moves when you talk.
I sometimes work with resin bases from other makers and usually their jaws work by pushing down on it with your chin.
The head above has no fan but when I add one it goes in the muzzle where that little triangle of firm foam is.
With most of my heads the only parts that actually touch you are the jaw, the hat and sometimes part of the neck. Your nose, most if not all of your neck, cheeks and ears are left untouched allowing airflow, minimizing the amount of sweat that gets soaked into the head, and creates a less claustrophobic feel. (Honestly I cannot stand a head made on a balaclava, it triggers my claustrophobia to have my head squeezed or my ears touched and I have to take it off)
The neck opens in the back and you simply slide your face in and fasten the velcro hat strap, this also allows one with glasses to get the head on without messing up their specs (I myself do wear glasses by the way) The neck closes via strong magnets glued into the folded over edge of the neck fur and thus the neck practically closes itself.
With most of my heads the neck connects from the ears back and the front of the neck gets pulled under your chin, this allows one to "pop the top" as in lift the face up like a welding helmet allowing you to take a quick breather or browse a vendor table without fully de-heading, that way if a kid rounds the corner while your top is popped it is super easy to slide it back down. This disconnected neck is not visible when worn at all as the rim is well covered by the overlapping cheeks and chin of the fursuit's face.
For an in depth look at how I use a hat with a resin base, with photo examples, please click this link.
inside a resin head
here is a look at how neck vision works
For an in depth look at the inside of a foam head including photo examples click this link
Here is a A look at how Quadsuit heads fit and how the whole thing works
An inside look at body suits
hand sewn padding pockets, I used to sue lycra but now I like neoprene
Here is an inside look at the room where I live and make things