A new study reinforces the increasing difficulty marketers face in trying to target their message to Millennials on linear TV. Almost one-third (30%) of all U.S. Millennials are cordless, meaning they never had cable, satellite or fiber optic TV service or have “cut the cord.” Broadcast radio, meanwhile, has maintained a full-bodied reach among this desirable demographic.

The new findings from GfK MRI’s Survey of the American Consumer show Millennials (ages 18-34) account for 43% of the “cordless” population. That makes the demo by far the largest generational subsection of the cord-free group. By comparison, only 16% of Boomers are cordless.

Untethered Millennials turn to streaming for their TV and video fix, helping services such as YouTube, Netflix, Hulu and Amazon Prime grow at a swift pace. In fact, they spend two-thirds (65%) of their viewing time streaming via a TV set or other device, putting them outside the grasp of linear TV. That’s nearly double the proportion for cordless Boomers (36%), who instead spend the majority (56%) of their viewing time watching live TV on a TV set over the air.

GfK MRI’s study also shows that Millennials are hard to reach because they’re 44 times more likely to be cord-free than the average U.S. consumer.

Broadcast radio, meanwhile, continues to touch more Millennials than any other medium. AM/FM had a monthly reach of 95% of persons 18-24 and 98% of persons 25-34 during third quarter 2016, according Nielsen’s Q3 2016 Total Audience Report. That’s 10 percentage points higher than Live+DVR/time-shifted TV, which reached 85% of 18-24s and 88% of 25-34s during the same period. A total of 29.79 million persons 18-24 and 41.90 million persons 25-34 tuned to AM/FM radio monthly, according to Nielsen. That put it ahead of the 26.23 million 18-24-year-olds and 37.20 million 25-34-year-olds reached by Live+DVR/time-shifted TV during the same period.

“One in three Millennials is living without a cord—so understanding this population is a major priority for advertisers and marketers,” said Karen Ramspacher, senior VP of Consumer Insights & Trends at GfK MRI. “These viewers are huge fans of quality programming and content, but they are not fond of being told where, when and how they should watch it….Appealing to this unusual combination of untethered living and discernment about content represents a sweet spot for marketers representing millions of brands worldwide.”

The findings come from GfK MRI’s Cord Evolution research and are based on around 25,000 respondents in its Survey of the American Consumer.