What Is a “Mil” in Sound Deadening?

Why It Matters, What It Means — and What’s Hiding Behind the Numbers

If you’ve been shopping for sound deadening materials, you’ve probably seen terms like 80 mil, 190 mil, or 225 mil. But what does mil actually mean? Is more always better? And what should you really be looking for?

Let’s break it down the right way — without the fluff.

📏 What Is a Mil?

A mil is a unit of thickness equal to one-thousandth of an inch:

1 mil = 0.001 inches = 0.0254 mm

So when a sound deadener says it’s 225 mil, that means it's 0.225 inches, or about 5.72 mm thick.

Just remember: mil ≠ millimeter — they’re completely different units.

📐 Quick Conversion Chart: Mil, Inch, and Millimeter

Mil	Inches	Millimeters (mm)
80 mil	0.080 in	2.03 mm
100 mil	0.100 in	2.54 mm
120 mil	0.120 in	3.05 mm
190 mil	0.190 in	4.83 mm
225 mil	0.225 in	5.72 mm

🔎 What Mil Is 3mm?

Let’s say you’re trying to compare by metric measurements.

1 mm = 39.37 mil So: 3 mm × 39.37 = ~118 mil

That means a 3mm-thick sound deadening material is roughly 118 mil thick.

additionally; 6mm-thick sound deadening material is roughly 236 mil thick

❗ The Catch: What Makes Up That Mil?

This is where the marketing tricks come in. Many products advertise high mil thickness — but stack it with layers that don’t contribute to structural damping.

Common materials used to inflate thickness include:

• Foam: Good for thermal or airborne noise insulation, but does nothing for stopping vibration

• Adhesives and fillers: Add bulk without adding performance

• Thin butyl layers topped with aluminum and foam to create a thick-looking product

  
  

If you want real damping, the mass and density of the actual damping material matter far more than the thickness alone.

🧠 A Real-World Comparison of Common Constructions

Here’s a breakdown of three common types of sound deadening constructions using actual specifications:

🧱 1. High-Mass Bitumen Polymer Mat

• Thickness: 225 mil (5.72 mm)

• Construction: Solid modified bitumen polymer with acrylic adhesive

• Aluminum: ❌ None

• Foam: ❌ None

• Weight: 2.45 lb/ft²

• ✅ 100% of the thickness is active structural damping material

• Built for maximum vibration control in high-performance applications

🧪 2. Premium CLD Mat

• Total thickness: 132 mil (3.35 mm)

• Construction: 120 mil butyl layer + 12 mil aluminum foil

• Foam: ❌ None

• Weight: 1.10 lb/ft²

• ✅ The aluminum foil constraint layer enhances damping efficiency

• A solid choice for broad automotive vibration control needs

🧻 3. Layered “3-in-1” Mat

• Total thickness: 184 mil (4.67 mm)

• Construction: 60 mil butyl + 4 mil aluminum + 120 mil foam

• Weight: 0.90 lb/ft²

• ❌ Only a fraction of the material is doing structural damping

• Foam is useful for heat and airborne noise but does next to nothing for panel vibration

  
  

📊 Side-by-Side Comparison

Type	Total Thickness	Core Damping Material	Weight (lb/ft²)	% Structural Damping
High-Mass Bitumen Polymer	225 mil (5.72 mm)	225 mil modified bitumen	2.45	100%
Premium CLD	132 mil (3.35 mm)	120 mil butyl + 12 mil foil	1.10	~100%
3-in-1 CLD + Foam	184 mil (4.67 mm)	60 mil butyl + 4 mil foil	0.90	~35%

note: some 3 in 1's get over 300 mil thick, don't fall for the fluff!

💡 Key Takeaways

• Thicker doesn't always mean better — not unless the full thickness is dense, functional material.

• Foam adds bulk but not vibration control — it may help with heat or airborne noise, but does next to nothing to stop panel resonance.

• Weight per square foot is one of the best indicators of actual performance.

• Check the breakdown — look at how much of the product is doing real damping (bitumen or butyl, how thick is the constraining layer (aluminum) etc.)

  
  

✅ The Pure Pressure Standard

At Pure Pressure Audio, we don't play the numbers game. VibraFlex 225 is built from the ground up with one goal: real-world vibration control through mass, density, and engineering.

• No foam.

• No gimmicks.

• No inflated mil counts.

Just honest specs, tested performance, and results you can feel.