Podcasts like This American Life and Serial attract millions of listeners in part because “a podcast is on-demand audio and on-demand is where it’s at,” said E.B. Moss, owner of marketing agency Moss Appeal and contributing writer at MediaVillage.com, at the recent IAB Mixx event in New York.

But audience size is far from the only reason marketers should consider podcasts.

To wit: In order to listen to a podcast, consumers must find and select a podcast, making an active decision to either download it or subscribe to it. And, further, most people listen to podcasts on portable devices, so they hear this content right in their ears, noted Mark McCrery, CEO of podcast advertising services firm Authentic, calling this “intentional listening.”

And that makes podcasts very personal content.

“It’s a coach on strategy or [a behind-the-scenes peek] during a trial or your favorite journalist on the backstory of breaking news — and they are right in your ear, whispering to you,” agreed Moss. “It feels like word of mouth and the listener is highly engaged and more likely than any other medium to do exactly what that medium tells them to go do.”

Further, Gina Garrubbo, president and CEO of National Public Media, said this intimacy, and its halo effect for brands, used to be the domain of public media because individuals wrote checks to their public stations and they felt warm and fuzzy when sponsors came on because there was a sense these brands love public radio, too. And that’s now the case in podcasting as well, she said.

“My initial thought on where podcasts fit into the media mix is there is a strong emotional connection,” Garrubbo added. “Once people start listening, it becomes their major way of consuming audio content. And it is a huge opportunity for sponsors to deliver messages in a very intimate, consuming environment. In world of 140 characters, people are listening to podcasts for an hour.”

And, according to JonPaul Rexing, senior director of sales at ESPN, the network doesn’t want to miss out and is expanding far beyond “just the stick and ball sports you may put to our name and logo.”

In other words, Rexing said one of the top election podcasts comes from ESPN.

“Podcasting allows us to stretch boundaries,” he said.

But what does this audience look like?

Per Garrubbo, NPR has nearly 27m weekly listeners and 65 per cent shared content. But, with podcasts, there are even more stories to share – and that’s among a young, affluent, loyal audience.

Further, podcast listeners are big consumers of social and subscription services and are used to lighter commercial messaging, Garrubbo said.

“They don’t necessarily need to be sold to,” she added. “Keep that in mind when it comes to dynamically served pre- and mid-rolls and host messages.”

In fact, Garrubbo described NPR as “jungle guides” for advertisers looking for the right show and host for their messages.

The Tech Guy, Leo LaPorte, for example, has a very popular podcast and his messages have at times brought websites down as listeners flocked to it, but LaPorte isn’t necessarily the right fit for every brand, McCrery said.

And when inbound marketing and sales software firm Hubspot sponsored Embedded, Garrubbo said the brand knew listeners were passionate about the podcast and kept its messaging short and sweet as a result: “We are proud sponsors of the Ted Radio Hour and know you want to get back to it,” she said.

McCrery said he looks at demographics to come up with good fits for advertisers looking for podcasts.

“We’re really a band of brothers, rooting for each other to win,” Rexing added. “So it’s important that this continues the momentum we’re on now.”