What is Backfill?

Backfill is a term commonly used in the online advertising industry to refer to the process of filling unsold ad inventory with ads from other sources. When a publisher has ad space available on their website or app that has not been sold to advertisers, they can use backfill to ensure that the space is not left empty and can generate revenue.

How does Backfill work?

When a publisher implements backfill, they typically partner with an ad network or an ad exchange that has access to a wide range of ads from different advertisers. These partners have a pool of ads that can be used to fill the unsold inventory. When a user visits a webpage or app that has backfill implemented, the system checks if there are any ads available from the direct advertisers. If there are no direct ads, the system then pulls ads from the backfill partner to fill the space.

Benefits of Backfill

Implementing backfill can bring several benefits to publishers:

1. Increased revenue: By using backfill, publishers can ensure that their ad inventory is always monetized, even if they are unable to sell it directly to advertisers. This can help maximize revenue potential.

2. Improved user experience: Instead of leaving empty ad spaces, backfill ensures that users are always presented with relevant ads. This can enhance the overall user experience and increase engagement.

3. Diversification of ad sources: Backfill allows publishers to tap into a wider pool of advertisers, increasing the variety of ads displayed on their website or app. This can help attract different types of users and cater to a broader audience.

Challenges of Backfill

While backfill can be beneficial, it also comes with its own set of challenges:

1. Ad relevance: The ads pulled from the backfill partner may not always be as relevant as direct ads. This can result in lower click-through rates and potentially impact the overall performance of the ad inventory.

2. Revenue sharing: When using backfill, publishers typically share a portion of the revenue generated from the ads with the backfill partner. This means that the publisher may not receive the full revenue potential from the ad inventory.

3. Control over ad content: With backfill, publishers have less control over the specific ads that are displayed on their website or app. This can be a concern for publishers who want to maintain a certain level of quality and relevance in their ad inventory.

Best Practices for Backfill

To make the most out of backfill, publishers can follow these best practices:

1. Choose a reputable backfill partner: Selecting a reliable and trustworthy backfill partner is crucial to ensure the quality and relevance of the ads displayed. Research and evaluate different partners before making a decision.

2. Optimize ad placements: Experiment with different ad placements and formats to find the most effective configuration for backfill ads. This can help maximize user engagement and revenue potential.

3. Monitor performance: Regularly analyze the performance of backfill ads to identify any areas for improvement. This can involve tracking metrics such as click-through rates, conversion rates, and revenue generated.


In summary, backfill is a strategy used by publishers to fill unsold ad inventory with ads from other sources. It can help increase revenue, improve user experience, and diversify ad sources. However, it also comes with challenges such as ad relevance and revenue sharing. By following best practices and carefully selecting a backfill partner, publishers can make the most out of this strategy and optimize their ad inventory.