Intro
When you are upgrading existing buildings or designing new ones with vapour‑open, breathable build‑ups, moisture risk is often the big unknown. WUFI® is the industry’s leading hygrothermal modelling tool for answering that question – and Sisalwool is one of the few natural fibre insulations included in its material database.
That means you can model our moisture‑regulating insulation directly in your simulations and design with greater confidence.
What is WUFI?
WUFI® (from the German “Wärme Und Feuchte Instationär”) is a specialist software package that simulates coupled heat and moisture transport through building components.
In essence, it lets you build up a wall, roof or floor layer by layer, apply local weather data, and see how temperature and moisture levels change inside that construction/building over months and years.
Unlike simple static “Glaser” calculations, WUFI uses real climate files - including temperature, humidity, rain and solar. It draws on material properties such as vapour permeability, liquid transport and thermal conductivity from its internal database or from user‑defined inputs. The result is a dynamic picture of how a project will actually behave in service, not just on paper.
Why WUFI is Important for Retrofit and New Build
For retrofit projects (especially on traditional or solid‑walled buildings) managing moisture is critical to both fabric durability and indoor air quality. WUFI helps design teams to:
- Assess interstitial condensation risk over time rather than at a single design condition.
- Understand drying potential after moisture, rain events or internal humidity spikes.
- Compare different build‑ups, vapour control strategies and insulation types before committing on site.
On new‑build, high‑performance and low‑carbon projects, WUFI supports robust detailing of complex junctions and high‑insulation assemblies.
By modelling realistic hygrothermal behaviour, it helps reduce the risk of mould, decay and under‑performing insulation - issues which can otherwise undermine both comfort and embodied‑carbon gains.
The role of the WUFI material database
At the heart of WUFI is an extensive material database containing datasets that have been measured and validated by software developers and accredited laboratories.
Each entry includes the hygrothermal properties needed for simulation - moisture storage, vapour diffusion, liquid transport, thermal conductivity and more - in a format optimised for the calculation engine.
You can add your own materials into WUFI, but only if you have solid test data and really know what each setting means. In reality, most people stick to the built‑in database because it’s quicker, less error‑prone and keeps results consistent from one project to the next.
Natural fibre insulations are still pretty thin on the ground in the WUFI database compared with mainstream products, which is why having Sisalwool in there really matters. It means designers who prefer vapour‑open, bio‑based materials can work with the same confidence and ease they’re used to when they pick more conventional insulation
Using Sisalwool in your WUFI models
Because Sisalwool now appears in the official WUFI material database, you can specify it in your simulations in the same way you would any other product.
A typical workflow looks like this:
- Open your WUFI project and define the climate conditions for your site using the appropriate weather file.
- Build up your wall, roof or floor assembly layer by layer, selecting materials from the database.
- In the insulation layer, search for “Sisalwool” in the material library and add the relevant product entry.
- Run the simulation over your chosen time period and review outputs
Because the Sisalwool dataset has been built and checked specifically for WUFI, you’re not guessing at things like moisture storage curves or liquid transport values anymore.
That makes comparisons between breathable build‑ups more trustworthy, helps you fine‑tune thicknesses and linings, and gives you stronger evidence for conservation officers, warranty providers and clients.
And if you’d like a hand reading the outputs, we can share spec packs, example build‑ups and CPD sessions shaped around how your practice works.
the sisalwool collection
