Bong Cleaning Brushes
Weed Wissen
Wool brushes for the bowl
The best compromise is probably a soft to medium wool brush, with or without a separate wool head. The latter comes in handy with bulbous acrylic bongs that have hard-to-reach “corners”, though it isn't strictly essential. Many seasoned bong cleaners swear by it, because acrylic's sensitivity means you can't soak it in bong cleaner for as long, so the brush matters more here than it does with glassware. In many cases the wool head lets you reach spots a conventional brush simply couldn't.
Cleaning the chillum
Things are a little less dramatic with the typical chillum brushes. Since the vast majority of chillums on acrylic bongs are made of aluminium, there's little to no risk of lasting damage. Any scratches don't matter much here either, as they'd only ever form inside the pipe where no one sees them. A thin to medium chillum brush is perfectly sufficient in most cases, and you can happily skip the pricey specialist brushes. That even holds for slide-bowl bongs (with a pull-out bowl and no fixed screen), although you can expect the chillum and the bong itself to get noticeably dirtier without a screen. That said, you should clean at regular intervals to counter a nasty layer of built-up grime. Even when the pipe looks clean again, long-standing residue leaves at least unpleasant smells (and therefore tastes) behind.
Cleaning the screen
The only case where metal or steel brushes belong anywhere near an acrylic bong is cleaning the screens (if you use them). Here the gentle wool-head brushes won't get you very far and you usually need to reach for something more persuasive. This is the one spot for the rough approach, ideally a steel brush. Usually a few strokes over the dirty screen are enough to get it ready to use again. It's easier if you let the screens dry out a little first so they no longer have oily residue on them. Beyond the easier handling, that also means you get less gunk on your fingers. Once the screen is dry, the ash and grime more or less fall off on their own (hold an ashtray underneath!).