Most display ads on a content page are visible for a second or two at most. The user lands, scrolls, and the ad passes out of the viewport before the demand-side platform records a viewable impression. Adhesion units are built to change that by staying fixed in view no matter how far the user scrolls.

Adhesion Ads

Adhesion ads are display ad units that remain anchored to the edge of the browser viewport as a user scrolls, keeping the creative in view throughout the session rather than appearing once and being scrolled past. Because the unit stays on screen, it consistently meets the MRC viewability standard of 50% of pixels visible for at least one continuous second, which display ads need to qualify for viewable CPM (vCPM) pricing. For publishers, that means adhesion inventory commands a price premium from advertisers who use vCPM bidding to ensure their budget goes only toward impressions that were actually seen.

What Is an Adhesion Ad and How Does It Work?

A standard display ad sits at a fixed position in the page layout. When the user scrolls past it, the ad exits the viewport and the impression timer stops. An adhesion ad uses CSS position: fixed to stay attached to the viewport edge, typically the bottom or side of the screen, regardless of how far the user scrolls.

The practical result is a unit that accumulates viewable impression time rather than losing it to scrolling behavior. If a user spends five minutes on a page, an adhesion unit at the bottom of the viewport is in view for most of that time, generating multiple viewable impressions across a single page session. Refresh logic extends this further: an adhesion unit can serve a new creative every 30-60 seconds to the same user, each refresh qualifying as a fresh viewable impression as long as the unit remains on screen.

The format goes by several names depending on the platform and the position. Adhesion ad, sticky ad, anchor ad, and rail ad all refer to the same underlying mechanism but differ in where on the screen the unit is anchored. The terminology varies by ad server and ad network, but the behavior and policy implications are consistent.

Advertisers increasingly use viewability as a buying criterion. Google Ad Manager's viewability guidance recommends positioning ads near the bottom of the visible screen, just above the fold, as the placement that consistently produces the highest viewability rates. Adhesion units take this principle further by keeping the unit in that zone permanently.

The Three Adhesion Ad Formats Publishers Use Most

Adhesion implementations fall into three categories that cover most practical use cases.

Bottom anchor. A horizontal unit fixed to the bottom of the viewport, typically sized at 320x50 on mobile or 728x90 on desktop. This is the format most publishers encounter first. It sits below the content as the user scrolls and remains visible throughout the session. On mobile, it is the most common form of sticky advertising because the screen dimensions make the unit a natural fit below the reading area without covering content.

Sticky side rail. A vertical unit anchored to the left or right side of the viewport, typically sized at 160x600 (half-page) or 300x600. This works on wider desktop layouts where the content column leaves empty space on either side. The unit does not cover any content and has no visible impact on reading flow. For publishers with desktop-heavy audiences and wide-format templates, side rail adhesion is often the highest-viewability placement available because the unit is never obscured and users never interact with it to dismiss it.

Sticky Stack. A format where new ad creatives load along a fixed track as the user scrolls, with older creatives seamlessly pushed out of view as new ones enter. This lets a publisher serve multiple unique impressions to a single user during one session without repeating the same creative. It is more technically complex than a static bottom anchor but produces more total viewable impressions per session.

Each format performs differently depending on device type, audience session length, and page layout. A bottom anchor that works well on a long-form article may interfere with a gaming tool where users interact with content at the bottom of the screen.

How Adhesion Units Affect Viewability (and Why That Changes Your CPM)

Viewability is measured by a standard set by the Media Rating Council and adopted across Google Ad Manager, DV360, and the programmatic supply chain. For display ads, 50% of the ad's pixels must be visible on screen for a minimum of one continuous second. For video, the threshold is two seconds.

Standard display placements fail this standard more often than publishers realize. Ads positioned near the top of a long page are frequently scrolled past before they finish loading. Ads placed at the bottom of the page often never enter the viewport at all. Ads placed in sidebars on mobile collapse to nothing, because mobile layouts typically drop sidebar columns entirely.

Adhesion units sidestep these failure modes by design. The unit is always in the viewport, so the viewability timer runs from the moment the creative renders. The only scenario where an adhesion unit fails viewability is when the page loads too slowly and the user scrolls before the creative has rendered: a page speed problem, not a placement problem.

The connection to CPM is direct. Advertisers who use vCPM as their buying metric bid specifically on inventory where they know the impression was seen. As the IAB's publisher viewability guidance notes, vCPM campaigns achieve significantly higher viewability rates than campaigns that do not filter by viewability, because buyers are self-selecting toward better-performing inventory. Publishers who supply that inventory attract those buyers and their higher bids.

The practical impact varies by publisher, but the mechanism is consistent: higher viewability rates make your inventory eligible for demand sources that exclude low-viewability supply. That is a larger addressable pool of advertisers at better effective CPMs, regardless of the absolute price point.

Adhesion Ad Policies: What Google and the IAB Require

Adhesion units are widely accepted, but they operate under specific policies that publishers need to understand before implementation.

Google's 30% screen rule: Google Ad Manager's guidelines for sticky ads require that a sticky ad must never cover more than 30% of the viewable screen at any given moment. A 728x90 bottom anchor on a standard 1,280-pixel-wide desktop viewport covers a small fraction of the screen, well within the limit. On mobile, a 320x50 unit at the bottom of a 667px screen height covers roughly 7.5% of the viewport. Oversized or custom implementations need to be measured against your actual viewport dimensions before going live.

Content must exceed ad area: The same Google policy requires that the content visible on screen always exceeds the area occupied by ads. A page where a full-height sticky rail and a bottom anchor together cover a significant portion of the viewport is a policy risk. Test your layouts across viewport sizes, not just the resolution you use for development.

User controls: The IAB New Ad Portfolio guidelines require that all sticky placements include a clearly visible close or minimize control. For bottom-anchored units, this is typically a small X or collapse button in the corner of the unit. Most ad server implementations include this by default, but custom implementations need to add it explicitly.

No autoplay audio: Adhesion units that include video should not play audio automatically. A sticky unit that remains on screen throughout a session and plays audio without user initiation is a user experience violation under both Google's policies and broad industry standards. It is also a practical problem: autoplay audio on a persistent unit causes users to leave the page immediately, eliminating any revenue benefit from the high viewability.

AdSense anchor ads: If you run AdSense rather than Ad Manager, Google offers anchor ads through its Auto ads feature. These are governed by the same 30% screen policy and require the same visible close control. Publishers using both AdSense and a header bidding partner need to ensure their combined ad load does not violate the viewport coverage limits.

How Gaming Publishers Get More from Sticky Units

Gaming and entertainment publishers operate in a context that makes adhesion units particularly effective. Users on gaming tools, companion apps, quiz sites, and browser game platforms tend to have longer average session durations than general content sites. A user checking a tier list, following a match stat, or completing a daily puzzle sits on the page for several minutes rather than reading an article and leaving. That dwell time is what makes adhesion inventory valuable: the unit accumulates viewable impression time that static placements cannot match on a shorter session.

The practical challenge is fitting the unit around the content. A bottom anchor that covers the action area of a mobile web game is a design problem before it is an ad problem. Gaming publishers need to map adhesion placements to the actual layout on each device type, confirming that the unit does not overlap interactive elements at any common viewport size.

Nitro works directly with gaming and entertainment publishers to optimize ad layouts, including improving viewability based on each publisher's unique site design. Our extensive portfolio of ad formats includes three pre-built, high-viewability solutions: Sticky Stack, which loads new creatives along a fixed track as users scroll, replacing older ads as they move out of view; Anchor, a fixed-position format designed specifically for mobile; and Sticky Side Rail, which is optimized for desktop layouts with space alongside the main content column. Each format is designed to meet viewability benchmarks without requiring publishers to build a custom sticky implementation from scratch.

Page speed is the variable that most often undermines adhesion unit performance on gaming sites. A publisher whose page takes four seconds to load on a mobile connection will lose the first impression on every session to slow rendering: the user scrolls before the unit appears. Nitro's infrastructure is built to minimize ad script latency, and publishers on the network see a 25% or greater improvement in page load times compared to their previous setup. Faster ad loading means more of the adhesion unit's potential viewable impressions are actually captured.

Tracking viewability at the placement level requires access to the right reporting. Nitro provides 100% transparent real-time reporting across all ad units, so publishers can see exactly what viewability rates their adhesion placements are producing and which formats are converting at a vCPM premium rather than standard CPM rates.

Frequently Asked Questions

What size should an adhesion ad be?

The most common sizes are 320x50 for mobile bottom anchors and 728x90 for desktop leaderboard adhesions. For sticky side rail units on desktop, 160x600 and 300x600 are the standard options. The right size depends on your layout and the viewport dimensions of the devices your audience primarily uses. Always confirm that the unit stays within Google's 30% screen coverage limit across all target viewport sizes.

Do adhesion ads hurt SEO or Core Web Vitals?

They can, if implemented incorrectly. A sticky unit that causes Cumulative Layout Shift (CLS) on initial load, plays autoplay audio, or covers a significant portion of the viewport will negatively affect user experience signals that Google tracks through Chrome. Properly implemented adhesion units, with reserved space in the layout and no intrusive behavior, do not damage Core Web Vitals scores. Reserve the space for the unit in your HTML before the ad script loads to prevent layout shift.

Are adhesion ads allowed on Google AdSense?

Yes. Google AdSense offers anchor ads through its Auto ads feature. These are subject to the same 30% viewport coverage policy that applies to Ad Manager implementations, and they require a visible close control for users. Publishers using both AdSense and a separate header bidding partner need to verify that their combined ad load stays within Google's policy limits.

What is the difference between an adhesion ad and an interstitial?

An adhesion ad stays in view continuously but does not block any content. An interstitial is a full-screen or near-full-screen ad that interrupts the user before they can reach the content they want. Adhesion units are persistent but non-blocking. Interstitials are temporarily blocking by design. The user experience, policy implications, and CPM profiles are different for each format.

How does an adhesion unit affect RPM?

Adhesion units increase the viewability rate of the inventory they occupy, which makes those impressions eligible for vCPM campaigns that carry a CPM premium over standard served-impression buying. The net effect on page RPM depends on your existing viewability rates, the demand mix in your ad setup, and how many sessions are long enough to generate multiple refreshes on the adhesion unit. Publishers moving from a non-sticky placement to an adhesion unit on the same position generally see measurable RPM improvement from that placement.

If you'd like to learn more about how Nitro can help you grow your revenue, get in touch with our team.

Nitro is dedicated to reinventing website monetization for the gaming industry. Our ad tech platform delivers uncompromised user experience alongside high performance revenue, with Net 7 payouts, same day support, and fully transparent real time reporting.