Soap bar vs liquid soap: which is really more sustainable?

You are standing in the drugstore or scrolling through an online shop and see two options: the familiar bottle of liquid soap, or a bar of soap without packaging. Both claim to be "sustainable." But which one really is? We compare the two based on five points that actually matter: packaging, ingredients, transport, shelf life, and skin-friendliness.

1. Packaging: plastic vs plastic-free

The most visible difference lies in the packaging. Liquid soap almost always comes in a plastic bottle with a pump. Even with recycled plastic and refill packaging, a piece of plastic is still needed per bottle.

A bar of soap does not have that problem. Most brands package their bars in paper, cardboard, or not at all. Some manufacturers even work with Cradle to Cradle packaging that is fully biodegradable, including the ink.

Winner: soap bar. If being plastic-free is the most important factor for you, this is the easiest and most visible step.

However, "liquid" is not by definition synonymous with fossil plastic. The Highland Soap Company For example, makes its bottles for shampoo, conditioner, and shower gel from sugarcane-based plastic (sugarcane plastic) instead of petroleum. It is still a bottle, but the raw material comes from a renewable source instead of fossil oil, and the bottles remain recyclable. For those who prefer to stick to liquid products but still want to reduce their fossil plastic footprint, this is a middle ground worth considering.

2. What's in it: SLS, sulfates and parabens

This is where it becomes less black and white. Both forms can be made with or without aggressive substances — it really depends on the brand, not necessarily on the block or liquid.

Regular liquid soap often contains SLS or SLES (foaming agents that can dry out the skin) and parabens as preservatives, necessary because a watery formula can promote faster bacterial growth. A bar of soap often does not require these preservatives: due to the low water content and the self-preserving effect of the pH value, bacteria can hardly multiply in it.

That does not mean that every bar of soap is automatically clean. Even hard, cheap bars of soap can contain SLS. So always check the ingredient list, regardless of the shape.

Winner: soap bar, with a caveat. The shape makes it easier to work without synthetic additives, but it is no guarantee.

3. Transport and CO2 emissions

An underestimated point: liquid soap consists of 80% water on average. That water is then transported all over the world, which costs extra fuel and therefore CO2 emissions. A bar of soap has a dry weight and is much more compact, meaning you simply get more washes per kilo transported.

Winner: soap bar.

4. Shelf life and ease of use

Liquid soap often runs out faster than you think: with every pump, some of it goes straight down the drain without ever having touched your skin. A bar of soap, provided you let it dry properly between uses, demonstrably lasts longer — some sources mention up to three times longer for comparable quantities.

In terms of ease of use, liquid soap does win on one point: no soap dish needed, no worries about a soggy bar. For on the go or in public washrooms, many people also find a pump dispenser more practical.

Winner: draw, depending on your situation.

This is also exactly the point where brands offering liquid products can reduce their footprint. In addition to their shampoo and shower gel bottles, The Highland Soap Company also sells refill pouches that allow you to refill a similar bottle about four times.This way, the ease of use of a pump bottle is retained, but you don't have to buy or throw away a new bottle every time — a middle ground between the convenience of liquid and the lower material impact of a block.

5. Hygiene: is a bar of soap really clean?

A persistent myth is that a bar of soap is less hygienic because it is touched by multiple people. In practice, this is unfounded: soap naturally has a pH value at which bacteria cannot multiply, as long as the bar is allowed to dry between uses. A soap dish with drainage (for example, made of cork, wood, or marble) is sufficient for this.

Conclusion: which one do you choose?

If sustainability in packaging and transport is your most important criterion, a bar of soap is the clear winner. If you are primarily looking for skin-friendliness, pay less attention to the shape and more to the ingredient list: avoid SLS/SLES and parabens, regardless of whether you choose a bar or a bottle.

So the most sustainable choice is actually: a soap bar, without plastic packaging, without SLS and without parabens — the combination that most conscious soap brands are already focusing on these days.

Would you still prefer to stick with a bottle, for example for shampoo or shower gel? Then look at brands that make the bottle itself more sustainable, such as The Highland Soap Company with their sugarcane-based bottles. This way, you combine the convenience of liquid products with a smaller fossil footprint.