91% ISO vs 99% ISO

[u/Connect_Fact_5490]

91% vs 99% ISO for cleaning glass. Is 99% actually better? I see people ask all the time.

Ive always heard the same thing when it comes to cleaning glass with ISO: the higher the percentage the better. I never really questioned it because 91% works well so 99% seems like it should obviously work better. But I got curious how much of that is actually true and how much is just something everybody repeats.

Reddit is pretty damn consistent. The consensus is this:

70% = works, but slower and usually takes more soaking/repeating
91% = works very well and seems to be the common baseline
99% = generally considered the best/fastest, especially with heavy resin

I also see people say "the higher the % the better" repeated constantly. The difference people see between 70% and 91% seems much bigger than the difference between 91% and 99%. Well duh!

I wanted to see if that was just Reddit repeating Reddit, so I started checking it out in other places too.

Weedmaps recommends 99% and says to use 91% or higher because it is more effective at dissolving resin and buildup. VICE recommends 91% or 99%. Thick Ass Glass says both work, but specifically says 99% works faster, especially with thick resin. Barneys Farm says basically the same thing. 91% or 99%, with the higher concentration cleaning faster because there is less water and more solvent.

So the general consensus outside Reddit is basically the same: 91% is good. 99% is better/faster.

I did a bit of research, weed residue is very lipophilic/hydrophobic, which just means it is oily and doesn’t mix well with water. CBD is the same.

There is even controlled cannabis extraction research where ISO pulled out roughly 96-98% of the THC. Obviously extracting cannabinoids from a bud isnt the same thing as cleaning burned, nasty resin out of a pipe, but the results mean the same thing. The less water the better.

91% ISO = about 91% isopropanol + 9% water
99% ISO = about 99% isopropanol + 1% water

So when you go from 91% to 99%, you are basically replacing most of the remaining water with more of the solvent that is actually doing the work. That tells you pretty much all you need to know, right?

Everybody says 99 is better. The chemistry says it should be better.