91% Alcohol vs 99% Alcohol


Fire hazard increase for sure. I wouldn’t use it in an ultrasonic cleaner.


Appart for legal liability and safety reasons - which, in my personnal opinion, is the main reason why Formlabs doesn’t officially recommends 99% solutions. IPA in real life situations is just as flammable as 90& as it is at 99% - you’ll dip your parts in something comprised of 10% of stuff you don’t want and that will not evaporate with the IPA. I’ll keep using 99% to get the cleanest parts.


I buy the 4 pack of 1 gallon jugs. It meets there minimum for Free Shipping. Plus it’s much handier that way. I have a Form Wash and that takes 2 gallons of IPA so you use it up much faster. Pouring the 32 oz. bottles is is a mess. Plus the 99% has a much longer life it seems.

I also buy spring water in the 2.5 gallon containers and pour that out into used 1 gallon water bottles. Then when I pump out the Form Wash it goes into those large containers. Again, much easier that trying to pump it back into 1 gallon bottles.

I haven’t yet, but plan to, recycle the IPA from the large container back to the Form Wash to see how it works after the residue has settled. Don’t expect as long a life but it still will be a savings.


Yeah good tips, I’ve actually got some left over 91% that I keep in old liquor bottles. I place them near the window I plan to reusethem after a good amount of settle.


I’ve just been using Yellow Magic 7 and Denatured. works just fine, cheaper.


I recall Formlabs recommended 99% back in the Form 1 days, but later reduced their advice to 90% and added this to their website:

Higher concentrations of IPA are available, but are much more hazardous to manage, while 90% solutions are safe for household use.

I tried to probe a little at the user conference to see if anything specific prompted the change, e.g. if they noticed employees getting symptoms or anything. The response I got was that they’re about equally effective and 99% will evaporate down to 90% pretty quickly anyway (not sure how authoritative that last part was).

I’ve been wondering about health effects from long term exposure to IPA vapors, especially after one user reported complications. Not trying to scare anyone, and Wikipedia says IPA is relatively non-toxic compared to alternative solvents. I wish I could find some kind of air quality monitor that measures concentration.

I appreciate all the expertise shared in this thread and will be watching it. For what it’s worth, I’ve been diluting mine to 90% lately with distilled water, and haven’t noticed any appreciable change in effectiveness.


I buy my IPA in quart sizes from Wally-World, and they list only two ingredients, IPA and water.


For what it’s worth I get IPA “100% 2-Propanol” by the gallon from Sherwin Williams. It’s about $25 per gallon, the manufacture number is R6K20. My local retail store doesn’t normally carry it but they special order it for me.


Here is the R6K20 safety data sheet for anyone who’s interested.


Been checking the prices for 99% IPA in gallon jugs from Zoro and other places, and at $26+ / gallon it’s $10-12 more than 91% IPA from Walgreens, which usually sell is for $4/quart or when on sale 2qt for $7.

Is the extra 8% worth the money? Not so sure. Someone mentioned that IPA found at pharmacies contains glycerine. That’s incorrect. “Rubbing Alcohol” does, but Isopropyl Alcohol does not. My bottle of 91% IP which I bought at Walgreens states that the active ingredient is isopropyl alcohol, and the inactive ingredient is purified water.

Anyway, when I get a “tacky surface” after a bath in alcohol, it’s time to change it. I still use the tried and true 2 tub cleaning procedure, and I rotate my tubs. One “dirty” tub for the main wash, and one “clean” tub for final soak. When the piece comes out of the “clean” tub and it’s still tacky, then it’s time for the “clean” tub to become the “dirty” tub, while the IPA in the “dirty” gets disposed of, and replaced with clean IPA, so it become the “clean” tub.


I hadn’t thought to rotate the clean tank to be the dirty tank… great idea. That will save me a lot of IPA.

And folks the primary difference between 99% and 90% is not inhalation health hazard- the fumes you breath are the same either way as it evaporates.
The difference is that 99% is a significantly higher fire hazard.


That’s correct - the only real difference is in fire hazard. This is especially a consideration if you are putting it straight in an ultrasonic cleaner.


Boom, baby! My local electronics shop felt pity on me coming in every month for five liters of IPA (I use it for other things besides printing) and started ordering it in ten liter bottles just for me, Approx. $43 USD.

And I’m probably not doing much to dispel the stereotype of East Europe and its alcohol. :wink:


I researched it for work years ago, we were using it as a cleaning agent and they had very strict chemical substance controls. That being said, I wouldn’t inhale it, i.e., maintain good ventilation, and I would wear gloves when using. Aside from people potentially passing out from inhalation, I could only find one instance of contact exposure, but the patient was soaking rags and applying it to their arms daily. Ignoring flammability concerns, I think the resin poses a greater health risk than the isopropyl.


I was just reading the warning on the left side of the label, I especially love the one about keeping it locked up and away from children. Also it’s for “Technical Use”, nothing about it being usable for disinfecting.

Most IPA I ever see is in pharmacies and is for disinfecting and cleaning.


I’d guess that’s because alcohol serves different purposes depending on its dilution. 100% isopropanol is a very low electrical conductor, so it’s used to clean electronic components and circuit boards (hence being called “technical” and sold in electronics hobby shops). Add 9% water and it becomes the medical disinfectant sold in pharmacies. At 30% and it becomes “rubbing” alcohol. The water is necessary to avoid drying ALL the moisture on skin. But chemically, it’s all the same exact alcohol. The labels are guides, not rules: “that water says ‘for drinking’, you can’t use it for boiling!”. :wink:


At what dilution is IPA safe to use in an ultrasonic cleaner?


Here is an interesting article on IPA in ultrasonic cleaners. The really interesting part, is the one dealing with isolating the IPA from the rest of the environment. Basically put the object to be cleaned in a container of IPA, and then floating the container in the cleaner tub which is 1/2 full of water, thereby isolating the IPA container from the actual metal tub.


If you want to be super cautious you can put the IPA in a ziploc bag (make sure it is thick enough with no leaks) and use water in your ultrasonic cleaner. Put your parts in the ziploc with the IPA then float that in the water. A very similar suggestion to Dudemeister’s above, but with much more available stuff (ziploc instead of beakers etc).

I know people who put 90% straight in the ultrasonic cleaner and haven’t had problems, but there’s never a problem until the first time (and catching on fire doesn’t sound like a lot of fun to me).


It has been replaced as a cleaner long ago. I read about similar.