Popunder

What it actually is

A popunder opens a new browser tab behind the active one. The user sees the ad the next time they switch tabs or close their current window. That is the entire mechanism. No interrupt, no in-flow injection, no banner real estate. The conversion economics work because the user lands on the advertiser’s full landing page with no preroll friction.

I spent five years at PropellerAds running iGaming books for Italy, Spain, and LATAM. Popunder paid the rent for that book — it still does for most tier-1 iGaming AMs you’d hire in 2026. The format is called “intrusive” in industry write-ups by people who have never bought a popunder campaign and don’t know which verticals actually convert on it.

Why advertisers keep buying it

• Highest eCPM in the entire display stack — at PropellerAds in 2023, popunder cleared €1.20–€3.40 CPM on tier-1 iGaming versus €0.40–€0.90 on banners for the same offer
• Click-triggered impressions survive most adblock setups that nuke iframe-rendered units
• Mobile and desktop, every OS — Android tier-2 popunder is where Adsterra and HilltopAds undercut PropellerAds by roughly 30%
• Zero website-side template work for publishers — adoption stays high because integration is a single script tag

What it is not the right format for

If your offer needs five seconds of consideration before the click — high-ticket B2B, complex SaaS, anything that needs an explainer above the fold — popunder is wrong. Push is wrong too. Native is the answer. I’ve turned this exact sale down at PropellerAds, mostly when the advertiser was a fintech that wanted “premium traffic” and didn’t realise their landing page took 4.2 seconds to first paint on a Brazilian 3G device.

Popunder is right for: iGaming deposit-bonus offers (Stake, Roobet, Betway-tier operators), sweepstakes, utility installs (VPN, antivirus), and tier-1 dating with a fast SOI flow.

Specs

• Pricing models: CPM and CPA. CPA-goal bidding is where SmartCPM earns its name — most tier-2 inventory converts cheaper on CPA-goal than flat CPM if you have enough postback volume to feed the optimiser
• Devices: Mobile and desktop. Mobile is roughly 70% of popunder impressions on Adsterra and PropellerAds inventory
• GEO coverage: 240+ countries, but the math only works in tier-1 and tier-2 for most verticals. Tier-3 popunder is volume without conversion outside utility installs
• Anti-fraud: Multi-layer filtering plus ML scoring on each impression. The honest answer: every network’s filter catches yesterday’s bot. The bot that converts at 12% in tracking and 0% in your CRM is always new