Latest / The Copywriting Podcast with Fexingo: Sales Letters, Headlines, and Persuasive Writing / How One Underlined Phrase Lifted Response by 34 Percent
Transcript
- Lucas: There's a direct mail test from the early 2000s — a financial newsletter publisher mailed a control package that was already generating a respectable 2.1 percent response rate. Luna: So a solid control. What did they change? Lucas: They took one phrase in the body copy — just five words — and underlined it. That was the only change. The result: response jumped to 2.8 percent, a 34 percent lift. Luna: One underlined phrase. That's it? No new offer, no different headline? Lucas: Nothing else changed. Same envelope, same letter, same order form. They just drew a line under five words. And it worked because underlining does something that bold and italic don't. Luna: What's that? Lucas: Underlining mimics the way we emphasize words in handwritten notes. When you underline something on paper, it signals 'pay special attention to this.' Bold and italic are typographic conventions — they're design choices. Underlining feels more like an instruction from one person to another. Luna: So it's almost like the writer is pointing directly at the reader and saying 'don't miss this.' Lucas: Exactly. And there's a psychological principle at play here called attention direction. The human eye is drawn to contrast. In a block of uniform text, an underlined phrase creates a visual anchor. The reader's gaze naturally lands there, even if they're just skimming. Luna: But why would that increase actual response? It's one thing to get someone to see a phrase, another to get them to act. Lucas: The key is what you underline. In this test, the underlined phrase was the single strongest benefit in the letter. It was the core promise. By underlining it, the copywriter made sure that even a skimmer would absorb the main reason to buy. And if that reason resonated, they'd go back and read more carefully. Luna: So it's not just any phrase — it has to be the most persuasive line in the letter. Lucas: Right. If you underline a weak or irrelevant phrase, you're just drawing attention to something that doesn't motivate action. But if you underline your strongest benefit, you're essentially giving the reader a shortcut to the decision. Luna: I've seen a similar effect in email subject lines. There was a test where adding an underline to a key word in the preview text lifted open rates by about 18 percent. Lucas: That's a great example. The same principle applies in digital. Underlining works because it's a learned cue. From school, we associate underlining with 'this is important, will be on the test.' That mental association doesn't go away. Luna: But in web copy, underlined text usually means a hyperlink. Doesn't that confuse people? Lucas: It can, but it depends on context. In a sales letter that's mostly plain text, one underlined phrase that isn't a link still stands out as intentional emphasis. The reader can tell it's not a link because it's surrounded by other text that isn't underlined. Plus, the underline color is usually black or the same as the text, not blue. Luna: So the key is to break the pattern sparingly. One underline per page, maybe two at most. Lucas: Exactly. If you underline everything, nothing stands out. The test I'm referencing only underlined one phrase in a four-page letter. That restraint is part of why it worked. Luna: Let's talk about the mechanics. In direct mail, underlining was often done by hand with a pen, or with a typeset rule. Does the method matter? Lucas: It does. Hand-underlining feels more personal — it looks like someone actually read the letter and wanted to highlight something for you. That can boost response further. In the test I mentioned, the underline was typeset, so it was consistent and clean. But I've seen A/B splits where a handwritten underline beat a printed one by a small margin. Luna: Makes sense. It's about perceived effort. A handwritten underline says 'I took the time to mark this for you.' Lucas: Right. And that leads to a broader principle: the format of the emphasis should match the medium. In email, you can use bold or color, but underline still works because it's unexpected. In a printed letter, underline is natural. In a landing page, maybe you use a different color background or a quote box. But the core idea is the same: direct the eye to the most important promise. Luna: I want to test this in an email for an upcoming campaign. We have a control email with a 12 percent click-through rate. If I underline the key benefit in the hero copy, what do you think would happen? Lucas: I'd predict a lift, but only if the benefit you underline is genuinely the strongest one. If it's just a feature, it might not move the needle. Also, make sure the underline doesn't look like a hyperlink — use a color that matches your text, or a dashed underline if your email client supports it. Luna: Dashed underline — that's interesting. Less likely to be mistaken for a link. Lucas: Exactly. Some email clients allow CSS text decoration style: dashed. It's a nice middle ground. But honestly, even a solid underline in the same color as the text works. People aren't that confused — they see the underline in context and understand it's emphasis. Luna: Let's zoom out. What's the bigger lesson here about copywriting? Lucas: The bigger lesson is that the smallest changes can produce outsized results when they align with how readers actually process information. A 34 percent lift from one underline — that's not about adding more words or making a bigger offer. It's about directing attention more effectively. Most copywriters focus on the headline and the call to action, but the body copy is where the decision happens. Underlining is a cheap, low-effort way to make sure your best argument isn't missed. Luna: And it's a reminder to test everything. I bet a lot of people would assume underlining is old-fashioned or irrelevant in the digital age. Lucas: Right. But the data says otherwise. And that's the value of this show — we dig into specific tests so you can take these ideas and apply them. Luna: Speaking of which, if these conversations have sparked a test you've actually run, or even just a new way of thinking about a project, that's exactly the kind of thing that keeps this show going. We don't run ads, and listener support is what makes that possible. Lucas: Yeah. If you've found value in these episodes, and you want to help us keep them coming without commercial interruptions, you can support the show at buy me a coffee dot com slash fexingo. That's buy me a coffee dot com slash fexingo. Luna: It's a small gesture that goes a long way. And we appreciate every single one. Lucas: Now, back to the underline. One more thing I want to mention: when you underline, don't underline the entire sentence. Underline just the key phrase — three to five words. That creates more impact because the reader's eye can take it in at a glance. Luna: So it's about precision. Underline the nuclear core of your benefit. Lucas: Exactly. And then test it. Run an A/B split. Measure the lift. You might be surprised at what a single line can do. Luna: I think I'll start with that email campaign. One variation with a single underlined phrase, one without. See what happens. Lucas: Let us know how it goes. We might cover it in a future episode. Luna: Alright, that's a deal. Until next time. Lucas: Thanks for listening, folks.