Why are the sides of plastic storage containers sloped?


Most large plastic storage containers like those produced by sterilite have sloped sides so that the top is wider than the base. This of course means that when placed side by side there is a large gap between them of wasted space. Is there a reason for this? Easier to manufacture? Structural integrity?

Edit: Thank you very much to all of you for your responses!

In: 94

14 Answers

Anonymous 0 Comments

Most of that is advertisement (in a way)

The container looks bigger from the top/front, so you think you get more for your money and are more likely to by that over the same product with a rectangular packaging

Edit: I thought you were talking about food packaging containers, not storage containers. Missed that….

Anonymous 0 Comments

Nesting is one reason.

When the top is wider than the base, you can place multiple empty containers inside each other in a very tight fit. If the top was the exact same size as the base, you would have to stack the containers on top of each other.

50 nested containers and 50 lids occupies much less space (on a pallet, on a shipping truck, in a cargo container) than 50 containers stacked on top of each other.

Manufacturing is the other: with a slight angle they will pull off of the mold easier.

Anonymous 0 Comments

It makes them easier to manufacture since they’ll pop right out of a mold – most molds require at least some draft angle to make them easy to get off.

It also makes them stackable during transit and in the store since they can nest inside each other.

Anonymous 0 Comments

So u/Buttleston has given a complete/accurate answer for this.

What I’d add is that shipping is important. The plastic containers take up a lot of volume and don’t weigh very much – so in industry terms, the trucks that transport them usually “cube out”, meaning the trucks are filled by volume and not by space. The trucks end up shipping a lot of air. So the final price to the consumer is affected by the trucking realities.

Anonymous 0 Comments


Anonymous 0 Comments

Same reason gold ingots or chocolate bars gave sloped sides. If you let gold, or chocolate or plastic solidify inside a mold, the item will be much easier to get out if the walls of the mold look like


as opposed to


Anonymous 0 Comments

Because you have to get them out of the mold. Pretty much all molded plastic parts have this draft angle, though it’s often well hidden so it’s not obvious just how the mold comes apart.

Anonymous 0 Comments

As others have mentioned, manufacturability is the big reason. As an engineer, I used to oversee the development of plastic injection molds in the automotive industry. There are ways to get around having obvious sloped walls and you can even have holes in the side walls of plastic parts. However, this adds a lot of complexity, weight, and cost. The fewer moving parts in a mold that satisfies all the requirements of the part being made, the better.

Anonymous 0 Comments

If you prefer vertical sides, look for milk crates, or their facsimiles. You’ll notice you can’t nest them, but they’re usually designed to interlock when stacked.

Anonymous 0 Comments

I’ve seen others mention it but the #1 reason for the lips on the container is for nesting. Warehouses want effect Storage space and like products that nest inside without creating a vacuum.

From an injection molding aspect I would argue it makes the mold much more complex due to needing lifters, sliders or other non standard injection mold components. It does add surfaces for injector pins though.