In December I started using only shampoo bars, having had two readers separately email asking whether the format was worth the switch. I'd tried bars three times before in a salon-professional capacity and been unconvinced. This was the first time testing as a regular user.
Four months in: it depends entirely on water hardness. In Melbourne CBD water (relatively soft) the bars perform comparably to liquid shampoos. In the harder water of regional Victoria where I spent two weeks in February, the bars were unusable — soap scum, wax-feeling residue, a noticeable difference in hair manageability within three washes.
The conclusion I'd publish if this were a full ranking is that shampoo bars are a defensible choice for consumers in soft-water cities (Melbourne, Hobart, parts of Sydney) and a structurally bad choice for consumers in hard-water cities (most of Brisbane, most of Adelaide, most of Perth). Brand marketing for shampoo bars never mentions this dependency, which is the part that should be uncomfortable for the category.
Glow will publish a full shampoo-bar category review in Q3 2026 that addresses this water-hardness factor explicitly. Until then: take the bar evangelism with the geographical caveat.