More than half the world's population uses fonts daily. Most people don't care about the internals, but some want to know whether there is a difference between TrueType and OpenType, or whether they can decide what font is best based on the file extension.

This article clears up the myths and misinformation about font formats that circulate online. The most common ones:

• Myth: .ttf means TrueType and .otf means OpenType.
• Myth: OTF is always more professional than TTF.
• Myth: a TTF can't contain OpenType Layout features.
• Myth: the file extension tells you the outline format.

By the end you'll see why each of these is wrong. First, some background on scalable font technology.

PostScript Type 1

Adobe launched PostScript Type 1 in 1984. It became very popular among desktop publishers, but it is now legacy — Adobe ended support for Type 1 in its own applications in 2023.

TrueType

TrueType was invented by Apple in the late 1980s as competition to Adobe's PostScript Type 1. It has been available since 1991 (Apple's Macintosh System 7). Apple licensed TrueType to Microsoft, and it became available on Microsoft Windows 3.1 in 1992.

OpenType

In 1994 Microsoft developed TrueType Open. It was improved jointly by Microsoft and Adobe to become OpenType in 1996. It is an extension of the TrueType font format, retaining its basic structure and adding many data structures that prescribe typographic behavior — ligatures, small caps, old-style figures, and more — which let font creators design better international and high-end typographic fonts. While TrueType only allowed TrueType outlines, OpenType also supports Compact Font Format based outlines (CFF is a variation of Type 1 fonts). OpenType solved many compatibility issues between Macintosh and Windows computers. Multiple Master support in OpenType was discontinued as of version 1.3 of the specification, but since 2016 it supports font variations (see below).

OpenType Font Collection

An OpenType Font Collection (formerly known as TrueType Collection) is a means of delivering multiple OpenType font resources in a single file structure.

OpenType Font Variations (also known as Variable Fonts)

In 2016, support for font variations was added to the OpenType specification. It allows multiple font faces within a font family in a single font resource — thin, regular, bold, and heavy, along with condensed and expanded, can live in one font file — and it allows continuous variation along the included design axes. The outline format can be TrueType or CFF based, but CFF-based variable fonts use a new internal CFF2 table. Because that CFF2 table is not backwards compatible, most font designers make TrueType-based variable fonts. The curve-format side of this decision is covered in TrueType vs PostScript: TTF, OTF & Curve Formats.

Web Fonts

The Web Open Font Format (both WOFF and WOFF2 versions) is a packaging format that encapsulates a TrueType font, OpenType font, OpenType font collection, or variable font. WOFF2 serves the same purpose as WOFF but uses newer, more efficient compression. Both are implemented in all major web browsers, although very old browsers might only support WOFF, or no web fonts at all.

Do TrueType Fonts Still Exist?

You can argue that OpenType fonts are all TrueType fonts with additional data structures. We prefer to see OpenType as a new format: yes, it's based on TrueType, but it is not the same.

If you accept that definition, then all modern computers mainly come with OpenType fonts. There are still numerous old fonts floating around the Internet that internally include only the data structures defined in the original TrueType specification, but it's best to avoid them, as they no longer meet today's design standards.

If you want to keep using the term TrueType for all OpenType fonts, then what's the use? It won't clarify anything. And if you want to call fonts with TrueType-based outlines "TrueType" and the ones with CFF-based outlines "OpenType," that's simply wrong — read the next section to see why.

Font File Extensions – TTF versus OTF

Type 1 is now legacy, and old "pure TrueType" fonts are not what modern font editors normally export. When FontCreator exports a .ttf with TrueType-based outlines, it is still exporting an OpenType font — just one with quadratic TrueType outlines. For modern desktop and web distribution, new fonts are almost always OpenType-based. So why do people still talk about "ttf" versus "otf"?

Probably because they think the file extension reveals the internal outline format. It doesn't, so let's explain.

Concerning glyph outline formats, OpenType fonts come in these flavours:

1. OpenType with TrueType-based outlines (quadratic Bézier curves)
2. OpenType with CFF-based outlines (cubic Bézier curves, like PostScript Type 1)
3. OpenType with both TrueType and CFF-based outlines (rare and not recommended)
4. OpenType with embedded bitmap-only glyph data, or color data without a normal outline fallback — specialized, and not recommended for general-purpose fonts

Some 25 years ago, Microsoft decided — mainly for compatibility — to keep the original TrueType file extension "ttf," but only for OpenType fonts with TrueType-based outlines. A new extension, "otf," was introduced and is allowed for both font flavours.

Because a file ending in .otf can be either an OpenType font with TrueType-based outlines or one with CFF-based outlines, the extension shouldn't be used to tell the flavours apart. Renaming a font file does not change the internal font data: well-written software should inspect the font contents rather than rely on the extension, although extensions still matter as compatibility conventions.

Here is what the official OpenType specification says:

"In all cases, software must determine the kind of outlines present in a font not from the filename extension but from the contents of the file."

Text Layout and Rasterizer

Font vendors usually provide several font resources to choose from, which makes it hard to tell which one you should use. So what matters?

Rasterizers take the glyph outlines and output them on a device. How good the output looks mainly depends on the rasterizer, the outlines, the font size, and optional hinting. Fonts usually look great on a high-resolution monitor and in print, but can look poor in an outdated web browser. So the quality and outline format you need depend on your situation.

OpenType Layout Features

Another very important part of a font is its OpenType features, which let text-processing applications improve text layout. Several of these advanced typesetting features are vital for complex-script fonts like Arabic, while others are used in desktop publishing and typesetting software such as Adobe InDesign to activate specific character variants. Not all software supports all OpenType layout features, so not all features are accessible everywhere. Note that these features can be present whether the font has TrueType-based or CFF-based outlines — they are not an "OTF-only" thing.

Internal Font Tables

Here is a technical summary of the internal font tables that identify specific characteristics of fonts:

Because all this information is buried deep inside the font, it's far more convenient to use a font manager like MainType to inspect it.

You can then make sure you're using the most recent version of your fonts, with the most up-to-date OpenType layout features.

Summary

If people tell you to use OTF over TTF, they probably don't have the full picture. If they're talking about file extensions, or "OpenType versus TrueType," or the internal outline format (TrueType-based outlines versus CFF outlines), that's not what TTF and OTF are really about — point them to this article. If what they actually want is OpenType layout features, then that's what they should be asking about.

Old pure TrueType fonts are legacy. For new work in FontCreator, choose between OpenType fonts with TrueType-based outlines and OpenType fonts with CFF/CFF2-based outlines. We like to compare a TrueType font to a square, and OpenType to an apex added on top — turning the square into a pyramid. The base is still a square, but when you see a pyramid, would you call it a square?

So a font's file extension is only a hint, not proof of the internal format. To be sure which outline format and which OpenType layout features a font carries, inspect the font internals — a font manager like MainType makes this easy. When you can choose between a font with TrueType-based outlines and one with CFF-based outlines, take the one with the best language support and sufficient OpenType layout features. And if your users rely on Microsoft Word and its PDF export, test font embedding carefully — TrueType-outline fonts are often the safer compatibility choice in Word-based workflows.

What to read next

• Which Font Format Should You Export? — the quick chooser for TTF, OTF, WOFF2, variable, and color.
• TrueType vs PostScript: TTF, OTF & Curve Formats — quadratic vs cubic outlines, in depth.