Plastic Density Chart: Compare Common CNC Machining Materials

As an application engineer at PlasticCNCPro, I spend my days helping customers choose the right plastic for their CNC-machined parts. One of the first questions we ask is, "What density does your part need to be?" Density affects weight, shipping costs, machinability, and even how the part performs in your assembly. In this article, I’ll walk you through a complete plastic density chart for CNC machining, answer common questions, and show you how to use density as a starting point for material selection.

What Is Plastic Density and Why Does It Matter for CNC Machining?

Density is simply mass per unit volume, typically expressed in grams per cubic centimeter (g/cm³). For plastics, this number tells you how heavy a given volume will be. But density is more than a weight metric—it influences several aspects of CNC machining:

Part weight and shipping cost: Lower-density plastics (e.g., PP at 0.90 g/cm³) produce lighter parts, reducing shipping and handling costs. Higher-density plastics like PTFE (2.2 g/cm³) are much heavier for the same volume.
Machinability: Dense plastics often machine more cleanly because chips are more rigid and break easily. Low-density, soft plastics (like LDPE) can be gummy and prone to melting or burring.
Heat dissipation: Denser materials typically conduct heat better, which helps reduce localized melting during machining.
Application suitability: A lightweight part for a drone needs low density; a chemical valve may need a dense, inert plastic like PTFE.

But density alone doesn’t tell the whole story. Always cross-reference it with mechanical and thermal properties—strength, stiffness, heat deflection temperature, and chemical resistance—to pick the right material.

Complete Plastic Density Chart for CNC Machining Materials

Below is a chart of common CNC plastics we machine at PlasticCNCPro. Density ranges vary by grade, additives, and crystallinity, so treat these as typical values.

|----------|----------------|----------------------|---------------------|

| ABS | 1.04–1.06 | Excellent | Tough, impact resistant, good surface finish |

| PVC | 1.35–1.45 | Good | Dense, chemical resistant, but can degrade |

| PET | 1.38–1.41 | Good | Strong, rigid, good dielectric properties |

Note: Density varies by manufacturer, fillers (glass, carbon), and crystallinity. Always request a material data sheet for your specific grade.

Which Plastics Are Best for CNC Machining? (PAA)

I’m often asked, “What plastic should I machine for my project?” The top choices are:

Acetal (Delrin) – My go‑to for gears, bushings, and bearings. Low moisture absorption, excellent dimensional stability, and chips break cleanly. Density around 1.42 g/cm³.
Nylon 6/6 – Strong, tough, wear resistant. Good for structural parts, but it absorbs moisture and can swell. Density ~1.15 g/cm³.
ABS – Easy to machine, impact resistant, inexpensive. Great for prototypes and housings. Density ~1.05 g/cm³.
PEEK – When you need high temperature (260°C continuous) and chemical resistance. Machines well with sharp tools. Density 1.32 g/cm³.

What about difficult plastics? PTFE is very dense (2.2 g/cm³) but soft and gummy. It tends to tear and deform during machining. UHMW (0.94 g/cm³) is tough but low stiffness—it can deform under clamping pressure. Both require special feeds, speeds, and tool geometry.

Plastic Density Comparisons: PP vs HDPE and Other Common Questions (PAA)

What is the density of PP vs HDPE?

PP: 0.89–0.91 g/cm³
HDPE: 0.94–0.97 g/cm³

Both are low‑density polyolefins that float on water. HDPE is slightly denser, stiffer, and more impact resistant than PP. For machined parts, HDPE gives better dimensional stability.

Which plastic has the highest density?

PTFE (Teflon) is the densest common CNC plastic at ~2.2 g/cm³. Next is PVDF at ~1.78 g/cm³. These dense plastics often require slower machining speeds and careful tool selection.

What is the most common material used for CNC tooling?

CNC tooling (cutting tools) is almost always metal—carbide, high‑speed steel, or diamond‑coated. But for the plastic workpieces, the most common materials we machine at PlasticCNCPro are Acetal and Nylon. They offer the best balance of machinability, strength, and cost.

Factors to Consider When Choosing a Plastic for CNC Machining

Density is just one piece of the puzzle. Here’s what I recommend you evaluate alongside it:

Mechanical Properties: Tensile strength, stiffness (modulus), and impact resistance. High‑density plastics tend to be stiffer, but not always—PTFE is dense yet flexible.
Thermal Properties: Heat deflection temperature (HDT) and coefficient of thermal expansion (CTE). Dense materials often have lower CTE and handle heat better, but check the data sheet.
Machinability: Chip formation, cutting forces, and achievable surface finish. A dense but brittle acrylic can crack; a dense but soft PTFE can smear.
Chemical Resistance: Density doesn’t directly predict chemical resistance, but high‑density crystalline plastics like PTFE and PVDF are among the most inert.
Cost and Availability: High‑density plastics like PTFE and PEEK are expensive. Lower‑density commodity plastics (PP, HDPE) are cheap but may lack strength.
Density Impact on Part Weight: For flying parts (drones, robotics) or weight‑sensitive assemblies, choose low‑density materials. For ballasts or vibration‑dampening, consider high‑density plastics.

Detailed Material Profiles Grouped by Density

Low-Density Plastics (0.89–1.2 g/cm³)

These are the lightweight workhorses:

PP, LDPE, HDPE, UHMW: All float on water. Great for food contact, low‑friction bearings, wear strips, and lightweight housings. Machinability is good to fair—low‑density grades can be gummy.
Nylon 6/6 (1.13–1.16): Stronger and more wear resistant than polyolefins. Absorbs moisture up to 2.5% by weight, so consider drying before machining.

Medium-Density Plastics (1.2–1.4 g/cm³)

Balanced properties, excellent machinability:

ABS (1.05): Tough, impact resistant, easy to glue/paint. Our top choice for prototypes.
Acrylic (1.19): Clear, UV stable. Machines beautifully but can be brittle—use sharp tools and avoid stress concentrations.
Polycarbonate (1.20): Extremely impact resistant. Can be gummy; use lots of coolant.
Acetal (1.41–1.43): My favorite. Low friction, dimensionally stable, easy to machine. Ideal for gears, bushings, and electrical insulators.

High-Density Plastics (1.4–2.2 g/cm³)

Stiff, strong, often high‑temperature or chemical resistant:

PVC (1.35–1.45): Dense, rigid, chemically resistant. Machines well but releases corrosive fumes—use proper ventilation.
PET (1.38–1.41): Strong, stiff, good dielectric. Used for insulators and mechanical parts.
PEEK (1.32): High‑performance, withstands 260°C, resists chemicals. Machines well with carbide.
PTFE (2.14–2.20): Absolute densest. Extremely inert, low friction, but very soft. Requires specialized tooling.
PVDF (1.78): High purity, good for semiconductor and chemical applications. Machines okay, but watch for heat buildup.

Design Considerations for CNC Machining Plastics

Over the years I’ve seen many parts fail due to poor design. Here are my tips:

Sharp corners: Avoid internal sharp corners—they create stress risers that can crack, especially in brittle plastics like acrylic. Use generous radii (R≥1.5 mm).
Tool selection: Use sharp, polished carbide tools with a high helix angle. This reduces cutting forces and heat generation. Never use dull tools—they cause melting and poor surface finish.
Cooling and chip evacuation: For low‑density plastics (PP, HDPE), heat builds quickly. Use compressed air or mist coolant. For high‑density plastics (PTFE, PEEK), chips can be abrasive—vacuum them away.
Fixturing and clamping: Low‑density plastics (UHMW, LDPE) deform easily under clamping pressure. Use soft jaws or vacuum fixturing. For dense plastics (Acetal, Nylon), clamping force is less of an issue, but avoid crushing.

Common Applications of Machined Plastic Parts by Density

Low‑density: Drone components, lightweight housings, food‑processing machinery parts, antistatic wear strips.
Medium‑density: Automotive interior parts, prototype enclosures, electrical insulators, gears, and bearings.
High‑density: Chemical‑processing valves, high‑temperature seals, pump impellers, semiconductor components, and PTFE gaskets.

Frequently Asked Questions (FAQ)

Can all plastics be CNC machined?

No. Very soft plastics (like thermoplastic elastomers) or those that melt easily (like some low‑density polyethylenes) are difficult. We can machine many engineering plastics, but some require special handling.

What is the biggest challenge when CNC machining plastics?

Heat buildup and chip welding. Plastics have poor thermal conductivity compared to metals. Heat can cause the material to soften, melt, or stick to the tool. Using sharp tools, proper speeds/feeds, and coolant is essential.

Why is moisture absorption important?

Some plastics, especially Nylon, absorb water from the air. This can cause dimensional changes (swelling) and reduce mechanical properties. For tight‑tolerance parts, store materials in a dry environment or machine them immediately after drying.

Are CNC machined plastic parts durable?

It depends on the material. Acetal and Nylon are very durable for bearing and gear applications. Acrylic and polycarbonate are impact resistant but can scratch. PTFE is soft but chemically inert. Always match the material to the loading conditions.

What is the density of PTFE?

PTFE has a density between 2.14 and 2.20 g/cm³. It is the heaviest common plastic we machine, which is why it’s often used for applications needing a dense, inert seal.

Conclusion: How to Use This Density Chart for Your Next Project

Density is a great starting point for selecting a CNC plastic, but it shouldn’t be your only criterion. Use the chart above to narrow your options, then cross‑reference with mechanical strength, thermal limits, chemical compatibility, and cost. At PlasticCNCPro, we recommend prototyping with a small piece of the material to test machinability and fit before committing to production.

I’ve helped hundreds of engineers choose the right plastic for their parts—sometimes it’s a lightweight UHMW wear strip for a packaging machine, other times it’s a dense PEEK seal for a chemical pump. The right density makes all the difference.

Need help selecting a material or getting a quote for your CNC‑machined plastic parts? Send us your drawing, 3D model, or application details. We’ll review your requirements and recommend the best plastic for the job.