So I’m one of the buyers that won’t be able to use my GF without the air filter. My estimated emails for laser and filter are Dec. 12, 2017 and May 4, 2018, respectively.
I’ve been looking for possible filter alternatives. I stumbled upon this blog post
https://hackaday.com/?s=breathe+easy
Is this design adequate? If so, is anyone interested in creating a kit that I (and others that might be interested as well) could assemble ourselves? Cost estimate?
Seems potentially problematic to put the finest elements of the filter, the auto filter, at the beginning of the exhaust path. If the charcoal is not encapsulated into its own separate container, I sure would hate to have to change the car filter and have 25 kilos of loose charcoal pellets to handle.
Also, most car filters are made of flammable fiber. If it catches fire from the laser exhaust, then entire unit would make a great forge for heating metal. Just catch the filter on fire to get the charcoal burning and keep the fan running to get it hot enough to melt / turn steel red hot at 2,000 degrees.
Fry some burgers and hot dogs on top while you watch! 
Has anyone thought to/attempted to make a water-based filter for one of the stages? I feel like as a first stage this could be very economical but I haven’t taken any time to research any sort of toxicity concerns.
I would argue that if you have a fire potential being exhausted by the Glowforge, you have a much bigger problem going on in the Glowforge itself… 
As a former fireman, small embers start large fires.
I can’t wait to see the design of the GF filter to see the composition of the material at the beginning of the exhaust path!
There are also disposable inline filters: https://www.amazon.com/Phresh-500-Inline-Filter-6-Inch/dp/B00CJIMUH2/ref=sr_1_5?s=lawn-garden&ie=UTF8&qid=1509905189&sr=1-5&keywords=inline+charcoal+filter&dpID=41N%2B%2B8ER05L&preST=SY300_QL70&dpSrc=srch
Either way you will need a booster fan, I opted for the quietest with longest warranty - the vortex 200cfm, but there are a wide variety of inline fans of all costs and quality.
I don’t believe you’ll have significant airborne embers being created by the Glowforge, navigating to the screened exhaust port of the Glowforge, traveling down a few feet of tubing, and having enough burn material left to ignite the filter.
I’m pretty confident that the amount of material flying off to make it that far would have to be significant, which would make the inside of your Glowforge look like a welding machine.
Maybe the reason the GlowForge filter has been delayed so long, even longer than the GF machine, is they took the design off the hack-a-day website and caught one of the early proto-type filters on fire
It says “Adaptable to any duct/filtering system” … does that mean that it is to be used with a vent out the window set up? I can’t vent out a window. The window is street-facing and our HOA (homeowner’s association) will not allow anything of that sort.
I saw a post on these forums where someone recommended using an old Rainbow vacuum cleaner for the start of the filtering process. It was too technical for me to make myself. I need a more plug and play type of set up. 
To my knowledge there is not anything at this point sanctioned by GF that does not still require venting to the outdoors. Having said that there are inline carbon filters that are 4" that are basically the same thing as the DYI you posted - however the whole filter is disposable. Again variety of quality/cost available on the googles…
https://www.amazon.com/TerraBloom-Australian-Scrubber-Hydroponics-Elimination/dp/B06WD3K8ZL/ref=sr_1_1_sspa?ie=UTF8&qid=1509911881&sr=8-1-spons&keywords=4+inch+inline+air+filter&psc=1
But like I said I don’t recall there being anything sanctioned by GF that doesn’t require outside venting.
This might work but the benefit of the Hackaday one is the huge surface are that 20kg of activated charcoal provides. But that’s nearly $100 by itself. The parts aren’t terribly sophisticated - CNC 1/2" ply or even two layers of 1/4" lasered would seem to work. Overall though it’s a few hundred bucks likely in parts, materials, shipping and a bit of profit.
Is an inline filter (plus possibly a fan) enough? Does the scrubbed air just exit the filter into the room? (Obviously, I’m a little confused how the inline filters work.)
The carbon and car filters I could source locally (if they’re GM filters I can even get a major discount 
)
After the discussion in this thread, I’m a little concerned now about fire, though. How substantial is that risk?
I used an indoor growing filter, like the one @tennessee_reid posted but larger (about 18 inches of filter) and there was some smell coming out of it, though it was much better than unfiltered - and while it cost a bit more, it was under $150 from Amazon. They’re a commodity part, sold in high volumes, so very cheap compared to specialty filters sold for laser cutters, which cost $thousands. But the results (at least, for me) weren’t anywhere near as good - with the commercial units, you smell nothing coming out a tall. So I’m viewing it as a temporary solution for use where I can’d vent (i.e. at a Maker Faire).
Hey there. Thanks for posting. How is the smoke on this one? I mostly cut and engrave eva foam for costuming with a little wood and acrylic here and there. My current studio unfortunately is without a window, so I absolutely can not be tripping smoke alarms.
Looking I see that the filter is just charcoal. it will get a lot of smoke but not the tiniest particles, and it would need a high volume fan in any case as the Glowforge fan is only adequate without back pressure.