Silicone bags leak if you overfill them.

Stasher-style silicone lunch boxes are leak-proof for yogurt and soup, but only if you keep the seal clean and don’t overfill them.

The seal is a simple press-down zipper, not a threaded lid. It works great for liquids when the edges are lined up and free of grease or bits of food. If any yogurt gets on the sealing surface before you close it, you’re asking for a leak. Same if you fill it past the “fill line” — liquid will find its way out when the bag gets squeezed in a lunch bag.

One thing nobody mentions: these aren’t meant for hot soup. The silicone handles heat fine, but pouring boiling liquid in means you have to close a very hot bag and risk steam pressure popping the seal. Let it cool first.

They’re also not indestructible. A pinhole puncture kills them, and I’ve seen the seal weaken after years of use.

So: yes, leak-proof for packed lunches. But “leak-proof” comes with a maintenance clause. Keep the seal clean, cool the soup, don’t overfill, and you’ll be fine.

Worth it for the reusable lunch bag, just don’t treat it like a Tupperware you can abuse.