We make a glass phin, so it would be easy for us to tell you glass is simply better. It isn't that simple, and we'd rather give you the real comparison than a sales pitch.
1. Heat retention
This is the one place steel has a real, measurable advantage. Stainless steel holds heat longer than glass. For a slow brew like a French press that steeps for many minutes, that gap matters a lot. A phin, though, is a different kind of brew: the whole cycle, from first pour to last drop, typically runs five to six minutes. Over that shorter window, the temperature drop in glass is far less consequential than it would be over a 20- or 30-minute steep. It's a real trade-off, just a smaller one than it sounds.
2. Flavor neutrality
Here, glass has the clearer edge. Borosilicate glass is inert. It doesn't absorb oils, doesn't hold onto old coffee residue, and won't ever contribute a metallic note to your cup. Stainless steel is food-safe and generally neutral too, but over months and years of daily use, it can develop a slight taste from built-up oils in a way that's genuinely difficult to fully scrub out. If you're precious about a completely clean, unchanging flavor from your equipment years down the line, glass ages better.
3. Drop Resilience
No contest. Steel wins. It doesn't chip, and you can drop it without a second thought. Glass requires more care, especially the delicate lid knob common to phin design. We stand behind ours (free replacement if it arrives broken, no questions asked), but if you're rough on your kitchen gear, that's worth knowing going in.
4. The ritual value
With steel, you pour water in and wait. With glass, you watch the bloom rise, watch the first drop fall, watch the color deepen as the coffee builds underneath. Functionally, the coffee that comes out might taste nearly identical either way. Experientially, it's a different ritual entirely — and for a brewing method that's supposed to be about slowing down in the first place, that difference is arguably the whole point.
So: if you want maximum heat retention and zero fragility, a good steel phin is a perfectly reasonable choice, and we mean that. If you want a phin that turns the process into something you actually watch and enjoy, and doesn't pick up flavor over years of use, that's the case for glass. And it's the case we built Bonsbons around.