Wigs Right wig fibre for ventilated wig

At that length, you're probably going to have to go with a synthetic monofilament. Most animal fibers have a much shorter staple length, and while human hair is (a pricey) option, you'd probably need to buy it pretreated to remove the cuticle, as it will otherwise tangle like the dickens.

I can't quite point you to the specific fiber you need, but I can say that you should probably avoid saran and polypropelyne doll hair, as they melt readily. I would also avoid yarn or ribbon derived fiber for melting reasons.Nylon and some doll kanekalon can be safe up to around400 degrees fahrenheit, but it is super important to test each batch with your individual heat tool before committing.

Cosplay hair is also not a great choice as it's often too thick at doll scale.

I have seen heat resistant doll hair on etsy and taobao before, so that would likely be your best bet outside of dedicated doll and reroot suppliers, but it is important to ask about the temperature rating because in some cases "heat safe" means "can be boiled" at most.

Cellulose based plant fibers like rose fiber, rayon, and viscose are also options, but I hear are very tricky to work with and style. Silk is also out there but a Bad Idea due to its floatiness and clinginess.

 

I would suggest kanekalon.

From my experience with Suri alpaca, it would be extremely thin and also very tangly for ventilation. And judging from the amount I use for a wig when using wefts, ventilated alpaca would end up extremely full bodied and floofy.

 

I've ventilated with suri alpaca a couple of times. You do have to be more aware of tangling and more aware of the direction you're knotting, but it isn't overly floofy.
Wefts do happen to use a larger volume of alpaca anyway.
this is a work in progress. I didn't like a bit of the front so removed it and replaced the removed part with some of the fabric I use for ventilating. Otherwise the entire front and center part is done using ventilating.
IMG_20220708_222756526 by hellsing365, on Flickr

 

It's an old Elfdoll Red head
I do my wig ventilating work stretched flat on a small embroidery hoop, then attach it to the wig base later on.

I finished the wig so wanted to share it;
IMG_20220714_172931328_PORTRAIT by hellsing365, on Flickr