Which Profile is better W20 or Janisol Slim 25 for the steel Doors?
Why Janisol Slim 25 Is the Smarter Alternative to W20 Steel Doors
When architects in the UK think “steel doors,” W20 often comes to mind. But is it still the best choice in 2025? Not quite.
At AtoZ Design and Glass, we’ve worked on over 100 bespoke steel projects across London. What we’ve seen is clear: W20 is outdated. The modern build demands better insulation, leaner aesthetics, and faster delivery.
Let’s break it down.
W20 vs Janisol Slim 25: The Technical Truth
FeatureW20 ProfileJanisol Slim 25 (Cold Profile)MaterialHot-rolled steelCold-formed steelThermal Break❌ None✅ Yes (polyamide barrier)GlazingSingle/DoubleDouble/TripleDesign LookIndustrial, chunkySleek, minimalistApplicationHeritage projectsHigh-end modern homesEnergy EfficiencyPoorExcellentLead Time16+ weeks (typical)12 weeks (guaranteed)CostHigher10% lower (AtoZ exclusive)
The Problem with W20 (That No One Tells You)
W20 was revolutionary in its time. But today, its lack of thermal break means:
Massive heat loss in winter
Condensation issues inside
Non-compliance with modern U-value standards
If you're building or renovating in 2025, specifying W20 could mean rework, complaints, or delays in sign-off.
Why We Recommend Janisol Slim 25
Janisol Slim 25—also known as Jamisol Cold Profile—is engineered for energy-conscious clients and high-performance builds.
✅ Thermally broken steel: Retains heat, lowers energy bills
✅ Ultra-slim sightlines: Matches or beats W20 aesthetics
✅ Custom finishes: RAL colours, corten, and stainless options
✅ Proven durability: Withstands 1,000,000+ open/close cycles
✅ Faster installation: Optimized for clean, fast site execution
Real Project: From W20 Spec to Janisol Success
One of our clients in South Kensington originally specified W20. Once we showed them the performance difference, they switched to Janisol. The result?
22% lower U-value
£3,500 saved in material and install costs
A stunning matte black finish that blends heritage with modern
Conclusion: The Future Is Cold
Steel doors are an investment. But W20 is an investment in the past.
Janisol Slim 25 is the future—energy-compliant, architect-approved, and built to perform.
