The Surprisingly Complex Design of the Ziploc Bag

You don’t know how to properly seal a resealable bag.

It’s not your fault. Pretty much everyone screws it up. People tend to close the zipper clumsily, allowing air into the bag. In the $1.6 billion resealable bag biz, air is public enemy No. 1. It leads to funkiness and spoilage and waste. No one wants that. That’s why Ziploc spends absurd amounts of time and money figuring out how to make sealing a bag (and opening it again) easy.

The company’s latest innovation is called, appropriately, the Easy Open Tab. It’s a small addition, but it builds on all that Ziploc has done since Börge Madsen invented the resealable bag in 1950.

Everyone takes resealable bags for granted, but there’s a lot of R&D behind them. Still, it’s difficult to see innovation unless you’re really, really into resealable bags. First came widetrack ribs in 1982, followed by a clicking zipper in 1993. Four years later, Ziploc added color to give the zippers—formed from melted polyethylene resin pellets—some aesthetic flair and a visual cue that the bag was sealed. The double zipper innovation of 2006 reinforced the seal and amped up the sound to ensure proper closure.

Each trick made using the bag easier. But the zipologists struggled to eliminate “thumb fumbles,” those maddening seconds spent trying to grasp the lips of the bag and get the damn thing open. To solve this problem, Ziploc engineers drew inspiration from a classic design: the envelope. A quarter-inch tab protrudes from the lip of the bag, providing a handle of sorts that makes it rip it open and devour your snacks. To help ensure your pizza doesn’t taste like garlic, a proprietary chemical recipe composing the bag’s film prevents flavor comingling.

U.S. Patent 7137736: Closure Device for a Reclosable Pouch USPTO

But it’s the zipper that really makes a resealable bag, and it’s taken Ziploc engineers ages to nail the design used today. Concepts are tested with CAD models, which are used to make zipper molds on steel plates. The zipper features microscopic J-shaped grooves (“hooks”) and arrowhead-like stems that interlock. Look closely at a double zipper bag and you’ll see this line of tiny teeth on the upper row, toward the lips of the bag. Running your thumb and forefinger along the track clasps the hooks around the stems. The zipper clicks at about 50 decibels to let you know you’re doing it right. But misalignment due to your clumsiness can create gaps.

So to solve this, Ziploc added a row of Xs and opposing convex dimples that create a haptic interface to guide your fingers for proper alignment. “I liken it to walking on a sidewalk with holes,” says one Ziploc researcher who can’t give his name because parent company SC Johnson won’t let him. “Suddenly there’s a hole and you step down and then you step back up and then down into another hole. [It] creates the sensation of the teeth—the bomp-bomp-bomp-bomp.”

Bruce Peterson

Combining the sound and feel of a zipper closing convinces you the bag is indeed sealed. And slightly rounding the hooks on the upper zipper made the seal four times easier to close than open. Ziploc also tweaked the second zipper, which prevents internal pressure from popping the seal. There, pointy opposing stems join together like hooks, a proven design that harkens back to the “Separable Fastener” patent Madsen obtained 65 years ago.

But there’s always room for improvement. And a coterie of engineers strives to unlock these secrets and give papa a brand new bag.