So, I just finished (well, good enough, still some details work todo) my fursuit head head. The weird thing with this head is that I'm using a technique I don't think anyone else have tried: using no glue in the head. This writeup explains what I did and what I learnt. Perhaps someone else can learn a thing or two from my findings/mistakes. Note that this is the first head I ever made (I've been doing a fair amount of cosplay before, though), so I'm sitll learning a lot.
I started following Matrices tutorials on making a fursuit head (great tutorials btw!), but when I came to gluing the foam, I realised that my foam was really hard to glue, maybe both due to my glue gun being extremely hot and the foam not being so dense as it should be. I decided to try and sew the foam instead, and realised it actually worked quite well. Then I thought "I wonder if I can make a head with no glue" and tried it out. These are my results. For images, you can find it in the folder Gaurian Head.

Making the foam base
I've been using the buckethead technique to make the base, with the exception that for all steps that says "glue" i said "sew". Other than that, it's basically the same thing. When sewing in the foam, I always sew with a high-strength thread using double threads and try to not tighten it too much around the foam, unless I would like to form a feature. I'm using a very nice plier to pull then needle through the foam if needed. It's a great save on my fingers to use a plier instead.
Generally, I was using the additive method, because removing material was kinda tricky since I had to be careful not cut them off while sculpting. This proved not ideal, as I didn't have as much freedom with sculpting as I would have liked to have. To hold the extra pieces in place while sculpting/fastening, I used normal pinning needles. If there was a feature that I wasn't happy with, I removed the sewn thread, re-sculpted and/or re-positioned the piece, and fastened it with thread again.

Patterning for furring
I used masking tape to create a pattern. Here, the procedure was also pretty standard. What I should have done was to put some plastic foil (the thing you use to preserve food) to make the whole tape-pattern stick together. One thing I noted, that was really helpful was to mark the fur direction A LOT on the pattern. This meant I had lots of lines and arrows that I could use to re-assemble the pattern after cutting it up.
One thing that was hard here was to actually get the pattern off. When cutting up the pattern, I had to really careful not to cut in the foam, and especially not in the threads keeping the foam together.
Once the pattern was free, I taped it onto some patterning paper and tried it on the head to ensure it would work. Some trimming and testing resulted in a pretty good pattern. When trying out the so that the pattern would fit properly, I used pinning needles to hold it onto the head.

Furring
Afterwards I converted my pattern to fur, ensuring to make as large single pieces as possible. Then I sewed (on the sewing machine) the patches together into a as large piece as I could. I furred the ears separately first, and then the rest of the head.
To fasten the fur, I used the same technique as when sewing together the foam. The method was generally finding the edge of the fur-patch and fastening it, as well as adding some stitches here and there. I tried using as short stitches as possible on top of the fur, and long stitches on the other side (inside the head, against the foam). This way, the thread is completely invisible when hidden in the fur, even on the places where it's shaved short. Using a long stitch on the foam side ensures a large surface area and not pulling the thread so hard on that side, to ensure that the thread doesn't cut through the foam.
Also, one thing i didn't realise was how big my head became after furring. I guess this is something you learn by experience. :)

Details
Unfortunately, I didn't have time to add so many details as I wanted to (the con was just hours away when I got this far). I lined the mouth by sewing some black fleece to the existing fur on the upper lips. For the lower jaw, I sewed a "pocket" on the machine with the fleece on side and the fur on the other side. I made it really tight, so I actually didn't have to fasten this!
The main problem with adding details was that it was hard to sew from one side to the other and to hide the thread when not working with fur. Therefore, I didn't add a proper lining to the eyes, which would have definitely looked better. But I made the eyes at like 1-2am, before travelling to the con, so they turned out OK I think ;) The eyes are made from a couple of layers of some very thin mesh fabric (I think the lady in the fabric store said it was Tulle), because the cross-stiching mesh I found was almost impossible to see out through. Since my eyes are quite small, I had to make the whole eye a mesh, to be able to see something out of the head. Fastening the eyes also proved quite hard, and didn't work extremely well.

Fastening the nose was also quite hard, since I really couldn't sew through the whole upper jaw. What I did was I sewed it onto the fur by compressing the whole nose before pushing through the needle. This worked OK, but maybe I should have tried using a curved needle instead.

Conclusion
It is possible to build a fursuit head completely without using glue. Since this was my first fursuit head and my first time working with this kind of more sculpty project I have nothing to compare to (doing what people "usually" do when making a foam head). My main durability testing consisted of travelling to and from Nordic Fuzzcon by train, keeping my head squished in a skiing bag, as well as wearing it during the con (not as much as I would have wanted though). After that, I think some thread might have come loose, but that's easy to fix.

Positive takeaways:
- I don't have to wait for glue to harden, meaning I can work faster
- I can work more safe and not risking burning myself on the hot glue (I did that once in the beginning oft he project)
- The foam head is extremely flexible, and therefore not very fragile it can be tightly squished, making it easy to pack.
- The fur was actually quite easy to fasten, and I don't have to it coming off due to high temperatures (would it ever get hot on your fursuit?!)
- I could do some thread forming of the foam "for free".
- The head is generally quite soft
- Thread does not age the same way as hot-glue does (yes, hot-glue doesn't age well!)
- I can easily revert fastenings, if needed to, without damaging anything severely

Negative takeaways:
- Building the foam base probably took more time than if I had used glue
- Sewing through foam is hard (my fingers are not quite happy...)
- There is some risk of thread coming loose (this actually happened) leading to the head breaking.
- Attaching details (especially the eyes) can be really hard, depending on the position.
- Glue is better suited to attach some details, especially when the details are not fur.
- All details must be sewable, to it will be hard to add for example teeth sculpted in some hard material (that cannot be sewn)

Future work
I want to add some more details, like fangs to the head. I'll also fix the eyes, since I wasn't very happy with them. I'll probably start using some glue on the head.
And finally, since I'm really weird, I'll add LEDs to my head, so that my white markings and eyes light up.

Final thoughts
Some of the techniques I've found, I will definitely continue using, but I will definitely use glue for certain parts. This was a really fun project and I'm actually very happy with my result, despite being my first head and me spending only about 4 days on it.