Consumers are increasingly skeptical of brands’ sustainability claims. Brands must be honest, transparent, committed and show urgency in order to build credibility with consumers, explains Wim Vermeulen, Director Strategy and Sustainability at Bubka, a Belgian advertising agency.

We know that the drive for greater sustainability will affect every aspect of what a company or a brand does. We also know that many consumers doubt the sincerity of companies' sustainability efforts. Because many are not yet convinced, they judge campaigns for sustainable products more critically than those for regular products i.e. products that do not claim to be environmentally friendly. Yet we create sustainable campaigns as we create them for regular products. And this is causing problems. Only 9.7% of the 100 sustainable campaigns we tested turned out to be credible for the consumers. So how do you advertise sustainability then?

Credibility is the key to effectiveness

Together with Prof. Dr. Gino Verleye of Ghent University, we examined what determines the effectiveness of sustainability communication. The outcome is that credibility is the key to effectiveness. Credibility and its determinants explain 59% of consumers' motivation to prefer sustainable products over conventional products. It also explains 30% of the purchase intention (next to price and quality) of a sustainable product. As a conventional product already exists for almost every sustainable product, success depends on whether a brand can initiate switching behaviour. Credibility is the crucial requirement for this.

Sustainable advertising starts with a disadvantage

Too often, there is a gap between what a company says and what it does. That creates the general perception that companies are not honest, even more so regarding sustainability. Only local companies are considered somewhat honest (46%), multinationals are not (13.7%). Even companies that call themselves sustainable cannot assume that all consumers believe they are (22.2%). Therefore, all advertising campaigns, even those from well-known sustainable companies, start with a disadvantage.

Which we reinforce by greenwashing

59% of the campaigns we tested show one or more characteristics of greenwashing. Almost half of the campaigns (46%) make very vague claims. A third make strong claims without substantiating why they are true. Whether it is intentional or not, it increases the disadvantage we already start with.

How to be credible when advertising sustainable products

Five elements emerge from the research, each in itself boosts credibility, and they also reinforce each other. Together they explain 72% of the variation in credibility scores. In the social sciences, a model is valid if it passes the 30% explanatory threshold. We can therefore confidently say that we have identified a model for sustainable advertising. What are the different elements of the model?

1. Be honest and transparent

We say that the bottle of a soft drink brand is 100% recyclable, although this is only true if we don’t count the caps and labels. We mention it, but only in the small print.

A banana brand says its bananas are carbon neutral. It also says they originate from Costa Rica. It creates the impression that the brand has made a serious effort to reduce its climate emissions. The truth is that emissions are offset, not reduced.

By hiding part of the truth, we only confirm what consumers already think: companies are not honest. Since honesty carries the most weight in earning credibility, being truly honest is the first thing we must do.

Case in point: Eco-Score, a front-of-pack label that measures the environmental impact of a product, was launched in January 2021 by a collective of ten French initiators. Colruyt is the first Belgian food retailer to apply the score to its own products and thus transparently show how well or badly its own products score. It is the best scoring campaign in the food retail category.

2. Show your brand is committed to sustainability

Only 7% of consumers trust their government to manage the sustainable transition. It is not surprising that 82% of consumers want companies to take the lead. If people feel that a brand takes sustainability seriously, 60% will believe what the brand says. The French supermarket chain Carrefour wants to prove its commitment to sustainability with its ‘Act for Food’ campaign by pointing out that it sells local products from 700 Belgian producers and that all the products come from a 40 km radius around the supermarkets. It’s the second-best scoring campaign with the food retail category.

3. Demonstrate urgency and take relevant action now

Consumers are aware that we live in a climate emergency. If a company shows that it understands the urgency and is taking action here and now, the credibility of its advertising increases. The Nespresso ‘Do you recycle with us’ campaign explains what happens when someone gives back their cups and how they are recycled and reused to make new cups. It doesn't make the spot that exciting, but it shows that it pays to return your used cups on your next delivery and that you can trust Nespresso to recycle them. It’s the best scoring campaign.

4. Create shared value

The Adidas x Parley commercial explains in detail how plastic sea waste is turned into yarn for trainers and how this helps reduce plastic ocean debris. The problem is relevant, so is the solution. Because it is a way for consumers to contribute, but on a larger scale than they can create themselves, it builds shared value. It is the most credible ad in its category.

5. God is in the detail

Although we are trained to focus on a single feature or benefit, this is not very helpful in building credibility. It seems that the more detailed a brand communicates, the more credible it becomes. In the 'Climate Action starts at home' ad, IKEA gives 16 tips on how to take care of the climate every day. It is the most credible campaign in its category.


Credibility determines the effectiveness of sustainable communication to a large amount. The credibility deficit is so significant that the persuasive advertising model is no longer applicable. We must find other ways. This is a proposal for a different model. Let it be the start of a discussion on how we communicate about sustainability. Because we must do things differently. The pressure from government, shareholders, activists, employees and consumers to do it right is increasing every day.

More details on this academic research and how it was carried out are available at