| Single-Walled Carbon Nanotube (SWCNT) | 0.7–1.4 nm | One cylindrical graphene wall | 1–20 µm | Approximately 1,000–20,000 | Can be metallic or semiconducting, depending on chirality | Very high along the tube axis; reported values vary substantially with defects, alignment, and measurement method | 90–99 wt.% carbon nanotube content, depending on purification level | Transparent conductive films, nanoscale electronics research, sensors, field-emission devices, high-performance composites | Chirality distribution, metallic-to-semiconducting ratio, residual catalyst, bundle size, dispersion quality, and length distribution |
| Single-Walled Carbon Nanotube (SWCNT) | 1.4–2.5 nm | One cylindrical graphene wall | 1–50 µm | Approximately 500–35,000 | Mixed metallic and semiconducting behavior; electrical performance depends strongly on sorting and alignment | High axial thermal transport; practical composite performance depends on interfacial resistance and network formation | 85–99 wt.% carbon nanotube content | Conductive additives, flexible electronics, electrochemical electrodes, structural nanocomposites, research-grade sensor platforms | Need for individualized tubes versus bundles, dispersant compatibility, surface functionalization, and acceptable amorphous-carbon content |
| Few-Walled Carbon Nanotube (FWCNT) | 2–5 nm | Usually 2–5 graphene walls | 2–30 µm | Approximately 1,000–15,000 | Generally conductive; electrical response depends on wall structure, defects, and network density | High axial thermal transport with good mechanical reinforcement potential | 90–98 wt.% carbon nanotube content | Conductive polymer compounds, electromagnetic-interference shielding, battery and supercapacitor electrodes, coatings | Wall-number distribution, outer diameter, aggregate size, defect level, bulk density, and compatibility with the host matrix |
| Multi-Walled Carbon Nanotube (MWCNT) | 5–10 nm | Typically 5–15 concentric graphene walls | 1–30 µm | Approximately 500–6,000 | Usually electrically conductive and less sensitive to chirality than SWCNTs | High axial thermal conductivity; effective composite values are lower because of tube-to-tube and interface resistance | 90–99 wt.% carbon nanotube content | Antistatic plastics, conductive adhesives, lithium-ion battery electrodes, supercapacitors, sensors, and thermal-interface compounds | Outer and inner diameter, catalyst residues, oxidation treatment, dispersion stability, and percolation threshold in the target formulation |
| Multi-Walled Carbon Nanotube (MWCNT) | 10–20 nm | Typically 10–30 concentric graphene walls | 2–50 µm | Approximately 200–5,000 | Typically conductive; performance is influenced by graphitization, defects, and contact resistance | High axial heat transport, with practical values affected by alignment and matrix adhesion | 85–99 wt.% carbon nanotube content | Conductive thermoplastics, rubber reinforcement, industrial coatings, EMI shielding, filtration media, and energy-storage components | Graphitization degree, tube length, powder flowability, moisture content, surface treatment, and regulatory documentation |
| Multi-Walled Carbon Nanotube (MWCNT) | 20–50 nm | Typically 20–60 or more concentric graphene walls | 2–40 µm | Approximately 100–2,000 | Conductive with comparatively robust current-carrying behavior in polymer and coating networks | Good axial thermal transport; bulk composite performance depends strongly on orientation and interfacial bonding | 80–98 wt.% carbon nanotube content | Large-scale conductive compounds, cement and ceramic additives, industrial rubber, shielding materials, and mechanically reinforced plastics | Lower surface-area-to-volume ratio than smaller tubes, dispersion energy, aggregate control, ash content, and processing equipment compatibility |
| Carboxyl-Functionalized SWCNT | 0.7–3 nm | One graphene wall with surface carboxyl groups | 0.5–20 µm | Approximately 200–25,000 | Conductive, but functionalization can increase defect density and alter charge transport | Usually lower than pristine SWCNTs because covalent defects interrupt the graphitic lattice | Typically 85–98 wt.% nanotube content, with functional-group loading reported separately | Water-dispersible sensors, biosensing platforms, membrane materials, polymer coupling, and aqueous electrode processing | Carboxyl loading, acid residues, pH stability, dispersion medium, tube shortening, and batch-to-batch functionalization consistency |
| Carboxyl-Functionalized MWCNT | 10–50 nm | Multiple concentric graphene walls with surface carboxyl groups | 0.5–30 µm | Approximately 100–3,000 | Conductive; oxidation treatment may increase contact resistance while improving interfacial bonding | Reduced from pristine MWCNT levels according to oxidation severity and defect concentration | Typically 85–98 wt.% nanotube content, with oxygen content specified separately | Water-based coatings, cement and polymer composites, electrochemical sensors, membranes, and functional nanocomposites | Oxygen content, acid-washing residues, pH, zeta potential, dispersion stability, tube integrity, and compatibility with the binder |
