Eco-friendly Zero-waste Air Purifier Filter?

I have a (desperately needed) air purifier that's not doing its job, because it's guts are clogged. The "pre-filter" is washable, but the inner pair of pleated hepa filters are not. At $30@ for 2 of something that's not cleanable or recyclable, that's not ok, with me! Plus, they're made in a place that I truly do NOT want to buy products from. I've no doubt I could make the casement for replacements, but I'm trying to figure out the material for the actual filter. The measurements for each are 10"×6.5"×1.5".

I have raw wool. A LOT of raw wool, and a bit of washed wool. I have alpaca and 'cashmere/angora' goat fiber. I don't know what it takes for something to be classed as a "hepa" filter. But, I'm 100% positive that I'd be easily able to make felt guts for my homemade casements. I'm thinking of a particular fleece I've been looking at since Christmas, because I've no clue what breed it is, so I'm not sure I'd want to spin it, anyway. But, I'm not sure how dense to make it, or whether I should blend the fibers for it, or if I'm just being ridiculous, and really ought to just pony-up the cash.

HEPA simply means High Efficiency Particle Absorbing. To meet a true HEPA classification, the filter needs to remove 99.97% of particles that 0.3 microns across. They are actually even more efficient at particles larger and smaller according to wikipedia - the 0.3 micron size being chosen as the reference simply because it is the hardest to capture.

https://en.wikipedia.org/wiki/HEPA#History

Basically, the material is made of very fine fibers in a random arrangement, and the tiny particles bump into the fibers and get trapped by static cling. It does not sound like vacuuming them out will help much, and washing actually makes them worse:

https://smartairfilters.com/en/blog/how-to-clean-wash-hepa-filter/

If the air purifier is doing a critical job, then you will be best served with a scheduled replacement of your filter. Could there be a way to mitigate the problem that the air purifier is solving? Selling your house and moving to a state with better air quality might not be cost effective compared to those filters, though :)

You might also look into electrostatic precipitators, which are filter-less, but I think they have their own drawbacks.

Finally, a DIY true HEPA is likely going to be a very tough project, but you might be able to cobble something together that is good enough. I would start with researching world war 1 era gas masks, which probably used the closest thing you will find to sustainable materials for a high efficiency filter. Let us know if you find anything interesting. Wildfire season will be here before long...

My only real option is the wool. I'm good with felting, and that's what the fibers look like, in the hepa filter. But, I'm not sure if I should blend them, or how densely. Hubs ordered new filters, for this time, which gives me some time to play with the project. After I was done writing the op, it occurred to me that I could use a blow dryer, to see if it was a good density. But, I think making a densely packed felt brick would probably work... I hope.

I make my own filters, I don't go for HEPA or the other criteria, I go for what can I do and clean or replace easily.
I'd suggest make felt that you can blow through, and do several stacked layers of it with space between them. I'd also put a cotton prefilter on it for the basic hair and dust bunnies. Rinse the cotton prefilter often, and pull off the top layer of felt and toss it when the air gets constricted, add a new one to the bottom.
The visual here is the top filters are taking the brunt of it, the next ones down each catch some of what's left, and the air spaces between them keep it from just being a block, when I layer filters I do better with gaps than blocks, a block tends to end up with the air only moving through a few paths, the air gaps make the air find different paths through each filter. Seems to increase the efficiency of each layer. And a block you have to replace the whole thing instead of just the top.

This is awesome info! Thank you! So far, we've been able to just wash the pre-filter, but when it dies, I'll definitely do that. I hadn't thought about the pathways, but that makes sense. I want to make the whole thing in such a way that, if I'm later unable to access the amounts of wool currently available, that I can still wash them. But, you've given me another idea - invariably, we discover the need to replace the filter at about the moment when we need it, most. A few extras - once I've got my new system fine tuned - would allow me to change it and do whatever it is that needs doing, while the dirty ones are being washed, and refreshed. Another benefit of making them from felt, is that I know using a small amount of essential oils on the felt won't damage my filters, like it potentially could, on these man-made fiber ones.