Facebook's Instagram is tripling down on story ads by letting brands create longer commercials.

Instagram Stories—the Snapchat-style section where brands and publishers post series of vertical videos that disappear in 24 hours—will now let brands create up to three videos in sequence, instead of the one 15-second video limit that was in place.

"With this, advertisers will now be able to tap into the same trends that are popular on Stories," Instagram said in its announcement on Thursday. The new look gives brands the ability to better blend into the rest of the stories rather than just looking like a commercial interruption.

Instagram says brands including Gap, California Pizza Kitchen, Netflix and Paramount were running the longer Stories ads during the rollout of the format.

Instagram is becoming a key platform for Facebook on a number of fronts, including as a counter to the popularity of Snapchat among younger audiences. And it's seen as inoculated from the types of problems affecting Facebook, like toxic political posts and false news.

As people spend less time on Facebook itself, apparently due to its recent algorithm changes, Instagram continues to grow in importance for advertisers. Sheryl Sandberg, chief operations officer at Facebook, highlighted the success of Instagram and stories on Wednesday, after Facebook announced quarterly results and the drop in time spent on its main property.

Sandberg said Instagram stories were "powerful" for the business.

"We're seeing these short-form videos work well in Instagram Stories, where people can watch a full-screen vertical video and swipe up to quickly learn about a product or brand," Sandberg said.

Sandberg said 60 percent of Stories ads were viewed with the sound on, which is important for Facebook as it tries to deliver more ads for brands that include the audio. On Facebook, autoplay videos often run with the sound off in the News Feed for most users, leading advertisers to lose a part of their creative toolkit.

Facebook does not disclose Instagram's ad revenue as part of its earnings report, but eMarketer estimates that the app will account for 18 percent of the company's revenue, with ad sales of $8 billion in 2018.

Instagram's Stories and the ease with which brands can buy ads through Facebook's platform are proving to be a challenge for Snapchat, which pioneered the disappearing vertical video format.

"Brands continue to flock to Instagram Stories," says Gemma Craven, ‎head of social and mobile at McCann. "It has become the place to experiment with ephemeral content and be able to measure results effectively. So this new unit will be a great addition to bolster a campaign."