No desk is complete without a pad of sticky notes, but have you ever given a thought to how sticky notes work? The science of Post-it Notes and other brands of sticky notepads is pretty fascinating—as well as no better demonstration of the idea that magic is science, and vice versa.
Sticky notes have been a part of our desktop landscape since the early 1980s. The Post-it Note brand from 3M is generally acknowledged as the first brand of sticky notes to have successfully been brought to market. These days, though, there are numerous brands to choose from, as well as a huge range of variety within those brands. From extra-sturdy sticky notes that will hold up even to the strongest breezes to the most adorably-shaped notepads you ever did see, sticky notes have proven to be the most versatile of office supplies, as well as a fun way to add some personalization to your workspace.
But how exactly do Post-it Notes work? Here’s a closer look at the inner-workings of the ubiquitous notepad.
A Short ‘n Sweet History of Post-it Notes
Before we can talk about how Post-it Notes work, we need to talk about how they came to be in the first place. And wouldn’t you know it? They were the result of a happy accident.
According to their most widely-accepted history, Post-it Notes saw their genesis in 1968. That’s when 3M research and development chemist Spencer Silver was spending his time at work trying to develop an extra-strong, extra-tough adhesive—and instead accidentally struck upon a polymer that created an adhesive that was less sticky than usual. Although he wasn’t sure at the time exactly how it might be useful, he knew that it could be useful if the correct application were found for it. So, he kept the idea in his proverbial back pocket, filing a patent for the adhesive in 1970 and receiving it in 1972.
Meanwhile, in the 1970s, 3M chemical engineer Art Fry was trying to solve a problem of his own: He sang in his church’s choir, but he couldn’t keep the paper bookmarks he used in his hymnal where he wanted them to be. Fry knew about Silver’s adhesive—Silver had spent some time following his initial discovery of the polymer attempting to get 3M on board with developing a product that used it, albeit unsuccessfully—and thought that maybe the solution to his problem might lie within it. Long story short, what started as sticky bookmarks eventually became sticky notepads—and although the resulting product’s initial limited launch in 1977 was a failure under its original name, Press ‘n Peel, a direct-to-consumers product trial campaign and a re-branding resulted in an enormously successful full launch in 1980. The product’s new name? Post-it. Because, well…that’s what you could do with one: You could literally Post-it anywhere.
The Proof Is in the PSA
The key to what allows for the posting and re-posting of these distinctive pieces of notepaper has to do with the unique characteristics of the adhesive Silver discovered.
The adhesive used for Post-it Notes and other reusable sticky notes of its ilk is what’s called a pressure-sensitive adhesive, or PSA (not to be confused with the other kind of PSA, the mighty Public Service Announcement). These kinds of adhesives are non-reactive and do not require a solvent, water, or heat to activate. They form a bond with the surface to which they’re being adhered when pressure is applied. Think, for example, of a self-adhesive stamp: When you press it to an envelope with your finger, the pressure is what adheres it to the paper beneath it. Pressure-sensitive adhesives can be made from a variety of materials; the one used for Post-it Notes is an acrylate polymer. (Indeed, 3M’s documentation terms their own Post-it adhesive a “Pressure-Sensitive Acrylate,” not just a pressure-sensitive adhesive.
Post-it Notes’ adhesive is also specifically a microsphere adhesive. As Mike Witte of adhesive manufacturer Franklin Adhesives & Polymers put it in a 2012 issue of trade magazine Converting Quarterly, microsphere adhesives are “the most repositionable type of pressure-sensitive adhesives”—that is, continued Witte, “they can be lifted and reaffixed repeated, without affecting the face stock or the substrate.” That’s what separates them from other kinds of pressure-sensitive adhesives: Microsphere adhesives aren’t just removable; they’re also reusable.
The Ins and Outs of Microspheres
So, what exactly is it about microsphere adhesives that allow them to be removed, repositioned, and re-stuck? As science writer and consultant Chris Woodford explains at the appropriately-titled website Explain That Stuff, it has to do with the fact that microspheres in question—which Woodford describes as “tiny glue bubbles”—are both much larger and much weaker than the glue bubbles found in other, more permanent PSAs. Because of the relatively large size of these glue bubbles, the adhesive film they form is discontinuous, which in turn limits the amount of contact between the glue bubbles and the surfaces to which they adhere. As a result, writes Woodford, “when you push a Post-it onto a table, some of these relatively large sticky capsules cling to the surface, providing just enough adhesive force to hold the weight of the paper in the little note—but not so much that you can’t peel it off again with ease.
(In contrast, adhesive manufacturer H. B. Fuller explains on their website, the adhesive film formed by the smaller glue bubbles used in “conventional emulsion adhesives” is “continuous,” which “in most cases [does] not allow for easy removal or repositioning.”)
But because Post-its aren’t meant to be permanent, their adhesive does lose its effectiveness the more you use it. As Woodford explains, “Every time you attach and peel off [a Post-it Note], dust and dirt attach to the adhesive capsules, so they progressively lose their stickiness.”
Furthermore, the adhesive works better under some conditions than others. According to 3M’s own documentation, factors that come into play when it comes to a Post-it Note’s ability to stick—and to keep on sticking—have mostly to do with the surface onto which the note is being stuck. The texture of the surface matters a great deal. For example, rough surfaces “[show] less points of contact for the adhesive” than smooth surfaces do, thereby making them less than ideal as Post-it Note landing spots.
The nature of the surface itself can also affect how well a Post-it Note sticks to it. If you’ve ever noticed that your Post-its tend to fall off of plastic surfaces more easily than they do, say, wood or paper, that’s because plastics often have certain chemicals present (“plasticizers” added to the material to improve its flexibility and cut down on the brittleness, for example) that can interfere with a Post-it’s ability to adhere to them. And lastly, anything that might be hanging out the surface that isn’t supposed to be there—think dirt or grease—can straight-up contaminate the adhesive.
The Downside of Sticky Notes
Of course, although sticky notes of all brands tout their usefulness in their ability to be removed without leaving any damage behind on the surfaces from which they’re lifted, they’re not always as damage-proof as they might appear.
According to a 2004 report from Chemical & Engineering News, chemist Susan Lee-Bechtold, then with the conservation branch of the National Archives and Records Administration, was asked to investigate the effects of sticky notes on paper records. She found that, on documents that had once had sticky notes stuck to them, charcoal dust tended to cling to the areas where the sticky notes had been adhered—no matter how long or brief an amount of time the note had been stuck there. She also determined that sticky notes could potentially leave “long-term stickiness” on paper documents and records, which might then cause further damage by inadvertently adhering these documents to other surfaces with which they come in contact.
That’s why, as The Atlantic pointed out in 2010, many libraries request that patrons refrain from marking books with sticky notes or flags. At the time, for example, the website for the University of California San Diego’s library preservation program actually had an individual page devoted to warning against the use of sticky bookmarks. “These seemingly harmless ‘markers’ leave behind their adhesive, even when removed immediately,” the page read. “DON’T be tempted to use them in books.”
So, don’t use sticky notes in library books or on the original copies of any important documents you might hold or come in contact with. But hey, if you find them useful for notes to yourself, to-do lists, or any other kind of personal use, go right ahead and Post-it. Just make sure you replace them every now and again!