What Is A Security Envelope?

Windowed envelopes have always been considered an official form of mail. They contain content like bills, credit cards, bank info, or paychecks. With these being the most common materials found in windowed envelopes, the security requirements are much higher than regular envelopes. But what is a security envelope, and how can security and personalization be achieved through using envelopes of this kind?

Security envelopes are designed to protect the privacy of customers – let’s learn how.  


Where did windowed envelopes come from?  

Envelopes have evolved throughout history, from clay tablets to the paper sleeves we use today. But paper envelopes were not originally designed with a plastic opening on the front.

Windowed envelopes were manufactured due to a lack of materials by Americus Callahan. Instead of using more paper for the entire face of the envelope, a small window was made. The film covering the window was made from hot oil, which enclosed the opening and protected the mail inside. In November 1901, Callahan patented his design so that we might all benefit from it.

Callahan's Patent

As Callahan developed the design of his envelopes, the window materials progressed from hot oil to rice paper to the clear plastic we use today. These kinds of envelopes have been more fully developed over time and have adopted different elements in order to create more security. They are now commonly known as security envelopes.


Why use windowed envelopes?

While regular envelopes are a staple for any office, here are a few reasons to grab some windowed envelopes, too.

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Save time

As your business grows, it can be difficult to keep up with customer correspondence on an individual basis. Instead of handwriting hundreds of business letters a month or printing addresses separately on individual envelopes, keep it simple: do all the printing on one page.

Print out the letters and the addresses on the same page and slip the properly folded document into your tinted envelopes. Make sure the address shows through the window! These steps make the process of company correspondence much more efficient.

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Save money

Time is money and when you’re saving time, you’re saving money. Your employees don’t have to spend hours handwriting addresses on envelopes; instead, they can use their time in more productive ways. You also save money by foregoing address labels and extra labeling materials by printing on one page.

Stand out Icon

Stand out

Windowed envelopes may be the standard for businesses, but you can stand out by customizing yours. Using windowed envelopes allows you to customize the window shape and size, which will make your letter stand out from the rest. Utilize that glossy windowed envelope and boost your brand recognition.

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Respect customer privacy

Businesses are required to respect the privacy of their customers in every form of communication. Postal privacy is extremely important and, in fact, required by law. The United States Postal Service has rules and requirements in place for anyone who handles another person’s mail.

In 1974, there was a Privacy Actpassed which laid out the rights and requirements of mail privacy and other private documents which might be mailed. Reading or opening mail not addressed to you has consequences, because it violates the privacy of the recipient. The business transactions between your company and your customer should be kept between the company and the customer. In order to protect this confidence, you can use security tint envelopes to avoid putting your customer’s privacy in danger.


How are windowed envelopes more secure?

Windowed envelopes are generally lined with a security pattern on the inside which creates a security tint. The pattern you see when you open your letter is security lined. Envelopes are usually manufactured with regular white paper, which makes it very easy for others to see what is inside; with these privacy tint envelopes, your company doesn’t have to worry about others infringing on you or your customers’ private transactions. Although the envelope inside pattern is designed differently on each envelope, they all accomplish the same goal: the privacy of the recipient.


Documents best suited for windowed security envelopes include:

  • Paychecks
  • Credit Cards
  • Bills
  • Medical documents
  • Legal documents
  • Bank statements
  • Insurance claims


While some security depends on the quality of the envelope, windowed envelopes will generally be more secure than standard envelopes. When you open a windowed envelope, there is usually some kind of pattern lining the inside of the envelope. This is the security envelope pattern which keeps information safe and sound within the envelope. These patterns are known as security tints and these tints may vary in style, but the most standard security tints are confetti-style and linen-style. 

Security Tint Graphic

Security pattern collections

Security Pattern Collections

Photo via Cotton & Flax


Talking envelope patterns may seem dull, but security envelope patterns have actually become a popular artistic element. The way the patterns complement each other creates interesting combinations and pieces. Individuals discuss their collections in personal blogs and security patterns are also featured in galleries and museums.

Milwaukee museum with security tint exhibit


Milwaukee Art Museum hosts a display of security tints which is interpreted as a representation of human life.

apartment decorated with security tints

Photos via Elizabeth Duffy


An apartment in New York City displays security patterns as decor. They are used as walls, curtains, bedding, and rugs.


Now you know why to use windowed envelopes, but how?

Windowed envelopes come in all shapes and sizes. They don’t all look the same, with a single window and a standard size. Mailing regulations and printed security envelopes can vary, but following the USPS requirements is a good rule of thumb:

  • Every character must be visible
  • The address must be printed on light-colored paper
  • There must be a clear 1/8-inch space between the text and the edge of the window during the entire mailing process
  • The window cannot come more than 1/8 inch into the bar code space
  • The window cover must be composed of transparent material in order to clearly read the content
  • The bottom edge of the window must be at minimum ½ inch from the bottom edge of the envelope


How to Use windowed envelopes graphic


While most envelopes being purchased are made to fit the postal regulations, it’s good to be aware of these factors so that you can avoid any mailing issues that might arise.


It’s true windowed envelopes help you save a lot of time by allowing you to print everything on one sheet of paper, but they aren’t too much help if you don’t know where to print your addresses. Here is a little step-by-step process that will align your text in the window of your envelope perfectly.


Step 1

Step 1: Open a Word document and click the “Mailings” tab.

Step 2

Step 2: Under the “Mailings” tab, choose the “Envelopes” tab.

Step 3

Step 3: A box will appear. Fill out the mailing address and the return address, and then click “Add to Document.”

step 4

Step 4: You’re good to go! When you print out that page, it will be in perfect alignment for your windowed envelope.


Check out our No. 10 envelopes blog post where you can access a free windowed envelope template designed just for No. 10 envelopes.



There are multiple sizes for envelopes you can use. However,envelope No. 9 and 10 are the most common. These envelope sizes can come plain, but you can also get them in windowed form. You can choose between the single window or the double window style in both sizes.  


Envelope dimension graphic


Although these are the most standardly used sizes for windowed envelopes, you also have the option of catalog envelopes with windows. Catalog envelopes can be useful if you need to mail larger documents, like medical or legal documents or a catalog which cannot be folded.


Security tint customization

Remember that although windowed envelopes are commonly known to be more secure than regular envelopes, it is not the window that makes the envelope more secure but the envelope inside pattern. As mentioned above, security tints have a pattern inside the envelope which makes it difficult to see within.

However, you aren’t limited to standard security tint patterns. Instead, you can choose to get custom-printed security envelopes. If you choose to get custom-printed security envelopes, you can incorporate a little bit of personality into your correspondence. This in turn can help with marketing efforts by building brand awareness and adding a feel of legitimacy to your business.

custom security tint


Use the Right Printer

Not every windowed envelope is compatible with every printer. If you’re planning on printing a return address in the corner, be careful you don’t melt the plastic of the window. Windowed envelopes are not compatible with laser printers, with the exception of specialty heat-resistant windowed envelopes. However – inkjet printers are perfectly compatible with windowed envelopes.


Window customization

As mentioned above, you also have the option to customize your window. If you want to add a little bit of company personality to your business letters, change the shape or size of your window. This allows your custom security envelope to stand out from the rest.


Custom Window image


While windowed envelopes help ensure the privacy of your customers, don’t forget to add a little personalization to remind them that your company is more than just a business. Add a signature line or a P.S. that reassures your customers they aren’t just another transaction.

While it is difficult to be passionate about envelopes in the same way you might be passionate about your company or your job, they’re still an important aspect of your company. You want to give your customers the best right down to the smallest detail. Choose a special envelope and who knows – maybe you’ll make a lasting impact on the recipient.


Enjoy this post about envelopes? Check out some of our other posts to help choose the best envelope.Want to know what kind of seal you should use for mailing documents? We’ve covered it! And, if you’re trying to figure out the right size of envelope to use, check out our envelope size and style guide.

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Calais Eledui is Blue Summit Supplies’ Content Writer. She is a full-time student studying writing at the University of Alabama in Huntsville. Writing is not just a job for her, but a way of life. While writing is a huge part of her life, coffee is huger. Coffee shop hanging, family-time talking, and Sunday afternoon napping are the only ways to get the best out of life.

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