The new shampoos come in a bar

Cruise down the hair care aisles in any big box store and you’ll see the usual lineup of liquid shampoos in plastic bottles, but there’s a new option gaining traction.

Shampoo bars are exploding in popularity, and with cosmetics giants like L’Oreal and Procter & Gamble offering solid shampoos through their haircare brands, they’re almost certainly here to stay.

How do they work? The same as liquid shampoo, just in a more concentrated form. Most liquid shampoos contain between 80 and 90 percent water — shampoo bars simply remove water from the equation and pack all the cleansing and conditioning agents into a solid chunk. But while a bottle of liquid shampoo might provide 30 or 40 washes, bar shampoos often last much longer — Klorane and Ethique both advertise that their bars last around 80 washes.

If you like a clean and uncluttered shower, shampoo bars are also a great space saver. A compact bar takes up much less space than a 12-ounce bottle, after all. And if you travel a lot, you can simply cut a chunk off a larger bar and stick it in any old container for a spill-proof shampoo that will last for weeks on the road and pass through airport security without a hitch.

Best yet, a bar will also never require you to fight with a bottle to extract the last few precious drops of shampoo. You simply use it until it’s gone.

To use a shampoo bar, simply wet the bar in the shower and lather in your hands before applying the lather to your wet hair. Then scrub and rinse like you would with liquid shampoo. For long or thick hair, you might want to rub the bar directly into your hair, but be conservative — a little really does go a long way. You can follow up with the conditioner of your choice or nothing at all if you prefer. Store your shampoo bar on a surface with adequate drainage, such as a bamboo soap dish. If you love your bar so much that you use it until it’s too small to grip, a soap saver bag will help you use those last chunks. Just drop the pieces into the bag, run it under water, and lather it up in your hands.