Type C vs Type X Gypsum Board: Key Differences for Fire-Rated Wall Systems

Type C and Type X gypsum board are both fire rated, and they are often quoted as if they were interchangeable. They are not. The difference lies in how each core behaves once it is exposed to fire.

The Differences at a Glance

Why the Difference Matters in a Fire

When gypsum is heated, it releases water of crystallisation and forms a protective layer. Higher-performing cores retain cohesion longer, resisting the shrinkage and cracking that would otherwise let heat through to the cavity. That is why two-hour designs frequently specify Type C rather than simply adding thickness of Type X — the mechanism is different, not just the quantity.

Selection Guide

• 1-hour partitions, ceilings, corridor walls — Type X, typically 15.9 mm
• 2-hour shafts, stairwells, compartment walls — Type C, or double-layer Type X
• Fire plus acoustic performance — Type C with mineral wool cavity insulation
• Wet and fire rated at once — combined dual-property panel

How to Choose Without Overspending

Across high-rise and healthcare projects, we have seen two-hour assemblies pass with Type C where the comparable Type X build-up needed an extra layer — the labour saved usually outweighs the panel premium, but only where the tested listing supports it. In the other direction, a one-hour requirement satisfied by standard Type X does not need Type C at all. Recommendations are tied to accredited laboratory fire tests and recognised assembly listings, and we do not extrapolate ratings beyond what has been tested. If a cheaper grade meets the requirement, we say so and send the test reference that proves it.

Frequently Asked Questions