Fire safety is one of the first things people worry about when using timber-based materials. After all, wood burns—so doesn’t that make wood fibre insulation a risk? Surprisingly, no. In fact, wood fibre can offer some real advantages when it comes to fire performance. Here’s how it behaves in a fire, and why that matters for your building.
If you’d prefer to listen to Chris and Andy talk about this very topic then just click play on the video below, where they discuss wood fibre and fire in episode 8 of Can I Just Ask?
The Fire Question: Does Wood Fibre Burn?
It’s one of the most common questions we get about wood fibre: what happens when it’s exposed to fire?
The short answer is yes—wood fibre does burn. It’s a natural, cellulose-based material, so it’s not non-combustible. But that’s only part of the story. When you look at how wood fibre actually behaves in a fire, things get a lot more interesting.
Slow, Predictable, and Less Toxic
Unlike many synthetic insulations, wood fibre burns in a controlled and predictable way. It chars slowly on the surface, which can help protect the structure beneath by forming a barrier that limits further combustion. This charring process can actually buy valuable time during a fire, giving occupants longer to escape and reducing the chance of structural collapse.
Toxicity is another key factor. Many conventional insulations—like PIR (polyisocyanurate) or some mineral wools—release highly toxic gases when they burn. Cyanides, hydrochloric acid and other nasties can be deadly to occupants and firefighters alike. By contrast, wood fibre produces far fewer harmful emissions. In complete combustion, the by-products are mainly carbon dioxide and water vapour. Incomplete combustion may release carbon monoxide (as with any wood), but the overall toxic load is far lower.
Not Fireproof—But Fire Smart
To be clear, wood fibre isn’t non-combustible. On its own, it typically carries a fire classification of E, which means it will ignite. That matters in situations where regulations demand non-combustible materials, like high-rise buildings or certain boundary conditions.
However, when combined with other materials in real-world building assemblies—such as wall linings or structural build-ups—wood fibre can perform impressively. Some internal insulation systems can achieve a classification of B, and in structural roles, wood fibre has been used in assemblies rated for 30, 60 or even 90 minutes of fire resistance.
In other words, it’s not about whether the material burns—it’s about how it burns, and what that means for the safety and durability of the building.
Rethinking Fire Resilience
There’s a common assumption that using non-combustible insulation will somehow “protect” a building in a fire. But in practice, when fire strikes, buildings usually have to be stripped right back—if there’s anything left to salvage. The more pressing concern isn’t just how the building survives, but how safe the fire is for people inside it and the crews who come to deal with it.
This is where wood fibre stands out. Its lower toxicity means fewer health risks for occupants, firefighters, and anyone involved in the clean-up. In fact, there’s growing concern about the long-term health impacts on fire crews working in buildings loaded with synthetic materials. Firefighters already face cancer rates significantly above the national average—and materials like PIR and plastic furnishings aren’t helping.
Fire Safety in Context
It’s also worth remembering that we fill our homes with combustible materials—furniture, soft furnishings, electronics—regardless of the insulation in the walls. So while the ideal is to slow down fire spread, what matters most is ensuring that the building’s fabric doesn’t add fuel to the fire or pump out a cloud of poisons in the process.
Wood fibre’s contribution to passive fire protection lies in this balance: it burns, yes, but slowly, predictably, and without the toxic plume.
Final Thoughts
Fire performance isn’t just about whether a material catches fire. It’s about how it behaves under stress, how much warning it gives, and how much harm it causes in the process. Wood fibre isn’t fireproof—but in many ways, it’s fire smart.
With careful design, wood fibre insulation can help meet stringent fire safety requirements while keeping the toxic load to a minimum. That’s not just good building practice—it’s good common sense.