What five materials which don't dissolve in water?

Why Some Things Just Won’t Mix with Water

Ever stirred sugar into your tea and watched it disappear? That’s dissolution in action. But not everything plays nice with water. Some materials, no matter how long you stir, simply refuse to dissolve. This happens because of how their molecules interact—or don’t interact—with water molecules.

Take sand, for example. Made mostly of silica, its molecules are tightly bound and non-polar, meaning they don’t attract water. No attraction, no dissolution. That’s why sand sinks to the bottom of your glass, unchanged.

Similarly, oil is a classic water-repeller. Its long hydrocarbon chains are hydrophobic—literally “afraid of water.” When you pour oil into water, it forms droplets or a separate layer, refusing to mix. This is why salad dressings need a good shake.

Now, here’s a twist: the original answer mentions vinegar as insoluble, but that’s actually incorrect. Vinegar, which is acetic acid dissolved in water, mixes completely with water—it’s very soluble. So vinegar doesn’t belong on this list.

Plastic is another stubborn one. Most plastics are synthetic polymers with strong, non-polar bonds. Whether it’s a grocery bag or a water bottle, plastic holds its shape in water because it doesn’t dissolve—thankfully, or our oceans would be even worse off.

And then there’s soil. While soil contains some water-soluble components, the bulk—like clay, silt, and organic matter—doesn’t dissolve. Instead, it may suspend temporarily or settle, but it won’t truly dissolve.

So, the real list? Think sand, oil, plastic, wax, and chalk. These stay separate, not because they’re magical, but because of basic chemistry: polar water molecules just can’t grab onto their non-polar structures. Some things, it seems, are better off staying apart.