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Picture two websites selling the exact same product at the exact same price. The first takes 8 seconds to load, piles on animations, and bombards you with pop-ups. The second appears instantly, gets straight to the point, and guides you intuitively toward your goal. Which one do you choose?
The answer seems obvious. And yet 40% of visitors still leave a site that is too slow or too heavy today. What's less often said? That the same high-performing site also consumes 13 times less CO2 than a conventional one.
Welcome to the world of eco-responsible UX/UI, where sober design goes hand in hand with business performance. And the figures speak for themselves: +17% conversion rate on average for eco-designed sites, and load times cut by 30%. Not bad for an approach sometimes dismissed as an "aesthetic sacrifice", is it?
Let's start by debunking a stubborn misconception: web eco-design has nothing to do with ugly, austere or dated sites. It's not a throwback to the 90s, with black text on a plain white background and nothing else.
Eco-responsible UX is the art of designing digital experiences that simultaneously optimize: technical performance (speed, fluidity), environmental impact (resource consumption), and user experience (satisfaction, conversion).
In plain terms? Less clutter, more efficiency. And that's something your users AND your planet love.
Before diving into the "how", let's look at the "why" with concrete data.
appYplanet 2024 study: Eco-designed sites show a conversion rate 17% higher than their resource-hungry competitors. Why? Because they're faster, clearer, and more pleasant to use.
Groupe Avril case: An eco-design overhaul cut the site's energy consumption by 30% while significantly improving business KPIs (bounce rate, session duration, conversions).
Amiens-based SME: By halving its site's weight, this company saw its conversion rate rise by 18%. The ROI? Immediate.
Strategic Data Solutions: Every euro invested in UX returns between €2 and €100 depending on the context. And eco-responsible UX, by optimizing further, tends toward the upper end of that range.
Google has hammered this home through its Core Web Vitals: speed is a major ranking factor. A site that loads in under 2 seconds is 3 times more likely to appear on the first page than one taking 5 seconds.
Web eco-design forces you to lighten the load: fewer JavaScript scripts, optimized images, minimal CSS. The result? Load times cut by 30% on average.
And every second saved counts: 1 second of delay = -7% conversions (Amazon study), 3 seconds of waiting = 40% page abandonment, 5 seconds = you've lost 90% of your mobile visitors.
Eco-design isn't a constraint, it's a performance optimization that mechanically boosts your business.
Dark mode isn't just an aesthetic preference. On OLED and AMOLED screens (dominant on smartphones since 2023), it cuts energy consumption by up to 60%.
But there's more to it: 63% of users prefer browsing in dark mode in the evening. Offering them this choice improves visual comfort, extends session time, and reduces eye strain.
On the business side? Sites with a well-implemented dark mode see an average increase of 8 to 12% in time spent on the site in the evening, prime time for many B2C SMEs.
67% of internet users now favor companies that display an environmental commitment. But be careful: they check.
An eco-designed site sends a coherent signal: you're not just talking about your CSR commitment, you embody it right down to your site's code. That's tangible social proof.
And the ease of use that comes from eco-design (short journeys, clean interfaces, focus on the essentials) matches exactly what your users are looking for in 2025: efficiency, not spectacle.
Designlab's Sustainable UX guide (2024) identifies three foundational principles. Let's break them down with concrete applications for SMEs.
The concept: Every element of your interface must serve a clear user goal. If it doesn't, remove it.
In practice: Ban carousels (only 1% of users click past the first slide, and they're heavy and slow down the site). Limit fonts to 2 maximum (Arial, Helvetica, Georgia). Simplify forms (each extra field reduces completion rate by 10-15%).
Use case: A Brussels-based e-commerce SME removed 5 fields from its contact form (going from 12 to 7 fields). Result? +34% completed forms within a month.
The concept: Offer an optimized dark mode, not just a color inversion.
In practice: Use dark grey (#121212) rather than pure black (#000000) to avoid eye strain. Adapt your contrasts (WCAG accessibility rules also apply in dark mode). Test your images, since some photos don't work well in dark mode.
Practical tool: The CSS prefers-color-scheme property automatically detects the user's preference. A junior developer can implement it in 30 minutes.
The concept: Inform your users of the impact of their actions and involve them in your approach.
In practice: Display your site's eco-score (via Website Carbon Calculator). Offer a lightweight version for mobile or slow connections. Indicate download sizes before the user clicks. Explain your approach on a dedicated page (transparency = credibility).
Inspiring example: KOBOK's website displays its carbon footprint in the footer. Simple, transparent, differentiating.
Images and videos account for an average of 60 to 80% of a website's weight. So they're your first lever for optimization.
WebP format: Adopted by 95% of browsers, it reduces image weight by 25 to 35% compared to JPEG without any visible quality loss.
Lazy loading: Only load images visible on screen. The rest load as the user scrolls. Immediate gain: -40 to 60% of data transferred on first load.
Smart compression: Tools like TinyPNG or Squoosh can reduce weight by 70% without perceptible degradation. Automate this process in your workflow.
Right-sized dimensions: Never serve a 3000px-wide image on a screen that will display it at 800px. Use responsive images (srcset) to adapt automatically.
Image checklist: ✅ WebP format (with JPEG fallback), ✅ 70-80% quality compression, ✅ Lazy loading enabled, ✅ Dimensions matched to display size, ✅ Alt attributes filled in (SEO bonus).
Videos are the heavyweight champions. An autoplay video on your homepage can weigh 50 to 200 MB. Ask yourself: is it really necessary?
Smart alternatives: Replace it with an image and a play button (loads only on click). Host on YouTube/Vimeo rather than locally (their servers are optimized). Limit quality to 720p for videos under 5 minutes. Offer a text transcript (accessibility + SEO bonus).
Edge case: If a video is genuinely essential on the homepage, limit it to a 10-15 second loop, compress it aggressively, and offer a pause button.
The General Reference Framework for the Eco-design of Digital Services, version 2 (May 2024), sets out 78 criteria across 9 themes. For UX/UI, 4 sections are particularly relevant.
Specifications (8 criteria): Eliminate non-essential features, precisely quantify user needs, respect accessibility principles from the design stage.
UX/UI (11 criteria): Limit the number of HTTP requests, favor graphic sobriety, avoid unjustified animations and autoplay, offer adaptive (responsive) design.
Content (8 criteria): Optimize media (formats, compression, dimensions), limit web fonts, avoid redundant content.
Frontend (16 criteria): Minify CSS and JavaScript, defer the loading of non-critical scripts, use browser caching effectively.
Eco-design score: The RGESN offers a rating system. A site reaching 75% compliance can display an "Eco-Designed Digital Service" badge, a significant commercial argument.
Practical tool: NumEcoDiag lets you evaluate your site for free against RGESN criteria. Allow 2 hours for a first complete assessment.
A pragmatic question for Belgian SMEs: which platform to choose if eco-design is a criterion?
Strengths: Clean, optimized code generated automatically, no plugins (=no excess code piling up), automatic image optimization (WebP, responsive), a fast global CDN included, average load times: 1.5 to 2.5 seconds.
Limits: Higher price than WordPress (from $29/month), a learning curve for the team, less flexibility on certain advanced features.
Verdict: Ideal for showcase sites, portfolios and marketing sites. Eco-design is facilitated "by design".
Strengths: Total flexibility via plugins, lower initial costs (hosting from €5/month), a huge community means solutions for everything.
Limits: Requires skills to optimize properly, poorly coded plugins mean bloated sites (easily 5+ MB per page), regular maintenance is essential, average load times: 3 to 6 seconds (depending on configuration).
Verdict: Can be very high-performing with the right plugins (WP Rocket, Imagify, Asset CleanUp), but requires expertise and maintenance.
KOBOK's recommendation: For an SME without an in-house IT team, Webflow offers a better performance-to-simplicity ratio for eco-design. WordPress remains relevant for complex projects with dedicated resources.
You can't improve what you don't measure. Here's your eco-design toolbox.
Google PageSpeed Insights: The classic. Analyzes performance, Core Web Vitals, and offers concrete recommendations. Aim for a score above 90 on mobile and desktop.
Website Carbon Calculator: Calculates your site's carbon footprint. The global average is 1.76g CO2 per visit. An eco-designed site aims for under 0.5g.
EcoIndex (Chrome extension): Grades your site from A to G on its environmental impact, based on 3 criteria: weight, DOM complexity, number of requests.
GTmetrix: In-depth analysis with prioritized recommendations. Excellent for identifying the heaviest scripts and images.
For a high-performing eco-designed site: ⚡ Load time under 2 seconds, 📉 Total weight under 1 MB per page, 🌱 EcoIndex: grade A or B, 🔋 Under 50 HTTP requests per page, ♿ WCAG AA accessibility score minimum.
Let's take a concrete example: the showcase site of a Walloon SME (B2B services sector).
Initial state: 15 pages, average weight: 4.2 MB per page, load time: 6.8 seconds, 127 HTTP requests per page, EcoIndex: grade F, bounce rate: 68%.
Actions taken (duration: 3 weeks): 1) Minimalist design overhaul (removal of decorative elements), 2) Migration of images to WebP + lazy loading, 3) Reduction from 5 to 2 web fonts, 4) Removal of autoplay videos (replaced with images), 5) CSS/JS minification + aggressive caching, 6) Migration to a Belgian green hosting provider.
Results after 2 months: average weight: 0.8 MB per page (-81%), load time: 1.9 seconds (-72%), 34 HTTP requests (-73%), EcoIndex: grade B, bounce rate: 41% (-40%), conversion rate: +23%.
ROI: Investment of €6,500, estimated gain in conversions over 12 months: €28,000. Return on investment in 3 months.
An eco-designed site isn't a dull site. You can have colors, well-crafted typography, quality photos. What matters is that every element is intentional and optimized.
Eco-design and accessibility go hand in hand. A simple site is by nature more accessible. But watch out for contrast (especially in dark mode) and HTML semantics.
Yes, speed matters. But not at the cost of brand identity or user experience. Find the right balance: a site loading in 2.5 seconds with a great experience beats a site loading in 1 second but impersonal.
Have you done the work? Say so! A "Our eco approach" page, an "eco-designed site" badge in the footer, a mention in your commercial offers. It's a differentiating asset, use it.
Eco-responsible UX/UI is not a passing trend, it's the future of the web. And for Belgian SMEs, it's a golden strategic opportunity:
✅ Measurable performance: +17% conversions, -30% load time
✅ Real savings: less bandwidth, cheaper hosting
✅ Commercial differentiation: a credible and verifiable CSR argument
✅ Better SEO: Google favors fast sites
✅ Higher engagement: more satisfied users, reduced bounce rate
The myth of a trade-off between beauty and performance is outdated. The best-performing sites of 2025 are also the most sober, the fastest, and the most converting.
The real question is no longer "Should we eco-design?" but "Can you afford not to?".
Ready to turn your interface into a sober, effective conversion machine? At KOBOK, we design digital experiences that combine modern design, technical performance and controlled environmental impact. From showcase sites to complex portals, we help you build interfaces that are good for your business AND the planet.
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