Shampoo soap and shampoo bar are not the same thing. Shampoo soap is made through saponification and has a high pH of around 9–10, which can make hair dry and coarse. A shampoo bar is solid shampoo made with a different formula than soap, and quality varies greatly depending on the manufacturer. FOAM’s shampoo bar is pH-balanced and formulated with a gentle, sulfate-free surfactant derived from coconut.
It is understandable that the terms get mixed up. Both are solid products for washing hair, and in everyday speech, shampoo soap is sometimes used as a general term for all solid shampoo products. But the difference in chemistry and effect on the hair is significant, and explains why experiences with solid shampoo products can differ so markedly.
Shampoo soap, shampoo bars, and liquid shampoo: the differences
| Feature | Shampoo soap (saponified) | Shampoo bar | Liquid shampoo |
|---|---|---|---|
| Manufacturing | Saponification of oils | Solid format; varies depending on the manufacturer | Liquid formula with water |
| pH value | High, around 9–10 | Varies depending on the formula | Varies depending on the formula |
| Surfactants | Soap salts | Varies; sometimes sulfates | Often SLS or SLES |
| Effect on the cuticle | Causes it to swell, resulting in dry hair | Depends on the pH and surfactants | Varies |
| Adjustment period | Often yes | Depends on the formula | Rarely |
| Suitable for all hair types | No | Depends on the formula | Depends on the formula |
Why does pH matter so much for hair?
The hair cuticle, the outermost protective layer of each hair shaft, needs a mildly acidic environment of around pH 4.5–5.5 to remain closed and smooth. Saponified shampoo soap has a pH of around 9–10. This causes the cuticle to swell and open with every wash, leaving hair feeling coarse and dry and more prone to frizz.
The pH of shampoo bars also varies depending on the manufacturer and formula. FOAM’s shampoo bar is formulated to be within the right pH range from the start, so the cuticle retains its natural smoothness and the hair feels soft straight out of the shower. Read more about how to wash your hair properly in our guide to using shampoo bars.
How can you recognize a good shampoo bar?
Looking at a solid shampoo product and wondering whether it is worth trying? There are three things to look for. The ingredient list can tell you a lot: choose a shampoo bar with mild, sulfate-free surfactants and avoid products containing soap salts (Sodium Cocoate, Sodium Palmate) or sulfates such as SLS. A good-quality shampoo bar will also state that it is pH-balanced.
FOAM’s shampoo bar cleanses with a gentle, sulfate-free surfactant derived from coconut and is pH-balanced to suit the hair’s natural environment. Read more about the differences between the various options in our guide to the best shampoo bar, and if you want to compare it with liquid shampoo, read more in our article about shampoo soap vs liquid shampoo.
Tip from foam.nu: Have you tried a solid shampoo product and noticed that your hair became dry or frizzy? This is probably because it was a saponified shampoo soap with a high pH, or a shampoo bar containing sulfates. Not all solid shampoos are created equal.
For an overview of all shampoo options, both solid and liquid, read our complete guide to shampoo bars and our shampoo guide.