Metal Substrate

Why Wall Thickness Matters in Metal Substrate Design

In exhaust aftertreatment, people often focus on cell density or coating technology. But there’s another detail that quietly shapes overall converter performance: the wall thickness of the metal substrate.

It looks small on a drawing, but in real applications, it affects flow, light-off behavior, durability, and even how stable the catalyst performs over time.

1. Flow Resistance Starts at the Walls

Thicker walls reduce the open frontal area (OFA) inside the substrate.

Less OFA means higher pressure drop.

For engines that need quick turbo response or steady airflow—especially modern small-displacement engines—extra flow resistance can show up as slower spool, higher fuel consumption, or slightly weaker efficiency.

Thin walls keep channels open, helping the exhaust move freely and maintaining the converter’s responsiveness.

2. Heat-Up Speed Depends on Mass

DOCs, TWC systems, and SCR catalysts all rely on fast light-off.

A wall that’s too thick stores more heat but requires more time to warm up.

This delays catalyst activation, especially during cold starts—where most regulated emissions occur.

A thinner metal wall heats up faster, helping the catalyst reach its working temperature sooner.

3. Mechanical Strength Still Matters

Metal substrates face vibration, thermal shock, and constant exhaust pulses.

Go too thin, and durability becomes the trade-off.

The goal is to find the sweet spot: thin enough to support efficient flow and fast heating, but strong enough to hold up under harsh operating conditions.

Modern metallic substrates use Fe–Cr–Al foils that allow thinner designs while still keeping high structural strength.

4. Coating Loading Must Stay Consistent

The wall provides the surface for catalyst coating.

If the foil is too thick or uneven, coating distribution may vary, eventually affecting catalytic activity.

Stable, precisely controlled wall thickness makes coating adhesion and uniformity easier to maintain, which is especially critical for close-coupled converters.

5. Thermal Fatigue Over Long-Term Operation

Engines heat up and cool down thousands of times.

Thicker walls expand differently and may create higher internal stress.

Well-designed thin-wall metal substrates handle those cycles more gracefully, reducing deformation and keeping long-term performance stable.

Wall thickness in a metal substrate isn’t just a design parameter—it’s a balancing act between flow efficiency, thermal response, and durability.

Choosing the right foil thickness ensures the catalytic converter performs consistently, meets emissions targets, and withstands real-world operating conditions.