Are Composite Doors Warmer than Timber? The Thermal Battle Explained

Category: Doors & Energy Efficiency
Reading Time: 7 Minutes

When the Hampshire wind is howling in January, the “style” of your front door matters less than its ability to keep the cold out. A common question we get in our Andover showroom is: “Are these plastic composite doors actually warmer than real wood?”

The answer lies in the core. Let’s strip back the surface and look at the pros and cons of each.

1. The Science: U-Values Explained

In the door industry, we measure warmth using a U-Value. This number tells you how easily heat escapes through the material.

The lower the number, the better the insulation.

• Old Timber Door: ~2.5 – 3.0 W/m²K (Poor)
• Modern Composite Door: ~0.9 – 1.4 W/m²K (Excellent)

2. Head-to-Head: Pros & Cons

To help you decide, we have analysed the strengths and weaknesses of both materials in detail.

3. The “Draught Factor” (Warping)

This is the factor most people forget. A door is only warm if it fits the frame perfectly.

Composite Doors use a Glass Reinforced Plastic (GRP) skin that is impervious to water. They do not swell, shrink, or warp. They stay air-tight against the rubber seals year after year, ensuring the heat stays in.

4. Security: GRP vs Wood

Beyond warmth, your front door is your first line of defence. Composite doors are widely recognised for their superior security features.

• Impact Resistance: The GRP skin (the same material used on lifeboats) is incredibly tough and resists sledgehammer attacks.
• Multi-Point Locking: Most composite doors come fitted with high-spec locking mechanisms that hook into the frame at multiple points.
• No Weak Points: Timber can have knots or grains that create structural weaknesses. Composite cores are engineered for uniform strength.

5. Lifetime Value: The 10-Year Cost

While timber might sometimes appear cheaper upfront, the lifetime cost tells a different story. Use our calculator below to check the real cost.

6. Which to Choose?

At KJM, we supply both. Here is our honest advice based on your lifestyle:

Choose Composite If… You want maximum durability, minimal fuss, excellent energy efficiency, and modern security with style, without the upkeep.

Choose Timber If… You prioritise traditional, natural aesthetics and are committed to the ongoing work (and cost) of regular maintenance to keep it looking its best.

Frequently Asked Questions