At One Place

Does it conduct electricity?

55 materials with whether they conduct and, for the 36 that do, how well — as a percentage of copper, which is the standard the industry actually uses.

Ranked against copper

IACS — the International Annealed Copper Standard. Silver, at about 105 %, is the only element above copper.
Material % of copper Note
silver 105% The best electrical conductor of any element, better than copper — and too expensive to use for anything but contacts and high-frequency plating.
copper 100% The reference standard. Every other conductivity figure is quoted as a percentage of copper.
gold 70% Slightly worse than copper, but it does not tarnish — which is why contacts and connectors are gold plated rather than made of it.
aluminum 61% About 61 % of copper by volume but far better by weight, which is why overhead power lines are aluminium: thicker cable, much lighter towers.
aluminum 6061 43% Lower than pure aluminium, because alloying always costs conductivity.
magnesium 39% Reasonable, but the metal is used for lightness rather than conduction.
aluminum 7075 33% Lower again.
tungsten 31% Moderate, and it is used for its melting point rather than its conductivity.
brass 28% Moderate. Good enough for electrical fittings where machinability matters more than conductivity.
zinc 27% Adequate, rarely used for conduction.
nickel 24% Modest for a metal.
iron 17% A poor conductor for a metal, about a sixth as good as copper, which is why it is a structural material rather than a wiring one.
platinum 16% Poor for a precious metal, used for its chemical stability instead.
tin 15% Poor, and mostly relevant as a solder constituent.
bronze 15% Modest.
chromium 13% Poor. Chrome plating is for appearance and hardness, not conduction.
wrought iron 12% Poor.
tin-lead solder (60/40) 12% Much poorer than the copper it joins, which is why a solder joint is a mechanical and sealing device rather than the conducting path.
lead-free solder (SAC305) 11% Similar to leaded solder and for the same reason unimportant.
mild steel 10% Poor, around a tenth of copper.
pewter 10% Poor.
high-carbon steel 9% Poor.
lead 8% A poor conductor, and heavy, so used for shielding rather than wiring.
tool steel 7% Poor.
tungsten carbide 5% Conducts, which is what makes it usable as an electrode material.
gray cast iron 4% Poor electrically, and also a mediocre thermal conductor — cast iron pans are prized for heat capacity rather than conductivity.
ductile iron 4% Poor.
Monel 400 3.5% Poor.
titanium 3% A remarkably poor conductor for a metal, about a thirtieth of copper.
stainless steel 304 2.5% Very poor, about 2.5 % of copper — worse than plain steel, because the alloying elements scatter electrons.
stainless steel 316 2.3% Very poor, marginally worse than 304.
mercury 2% A very poor conductor, and the only metal that is liquid at room temperature — which is what old tilt switches used it for.
Inconel 718 1.4% Very poor.
Ti-6Al-4V titanium alloy 1% About one per cent of copper — among the poorest conductors of any structural metal.
unidirectional carbon fibre composite 1% Conductive along the fibres, which surprises people who assume a composite is plastic. It is why carbon fibre laptop shells need care around electronics and why lightning strike protection is a real design problem on composite aircraft.
graphite 0.1% The exception among non-metals: graphite conducts because each carbon atom has a spare electron delocalised across the sheet. Diamond, the same element bonded differently, is an insulator.

The ones that surprise people

  • Silver conducts better than copper. It is not used for wiring because it costs a hundred times more and tarnishes.
  • Aluminium is only 61 % as conductive as copper by volume and far better by weight, which is why every overhead transmission line is aluminium and no house is wired in it.
  • Diamond is an insulator and the best thermal conductor known — five times better than copper at moving heat while moving no current at all.
  • Graphite is the same element and conducts electricity well, because its layers leave one electron per atom free.
  • Carbon fibre conducts, which makes lightning protection a real design problem on composite aircraft.
  • Stainless steel is a very poor conductor, around 2.5 % of copper — worse than plain steel, because the alloying elements scatter electrons.

Everything

Material Verdict Note
mild steel Conducts electricity Poor, around a tenth of copper.
aluminum Conducts electricity About 61 % of copper by volume but far better by weight, which is why overhead power lines are aluminium: thicker cable, much lighter towers.
water Does not conduct Pure water is an insulator. Tap water conducts because of dissolved ions, not because of the water — which is why the electrical hazard from water is really a hazard from what is in it.
copper Conducts electricity The reference standard. Every other conductivity figure is quoted as a percentage of copper.
gold Conducts electricity Slightly worse than copper, but it does not tarnish — which is why contacts and connectors are gold plated rather than made of it.
titanium Conducts electricity A remarkably poor conductor for a metal, about a thirtieth of copper.
concrete Does not conduct Insulating when dry, semi-conducting when wet, which is why concrete floors are treated as conductive for electrical safety.
stainless steel 304 Conducts electricity Very poor, about 2.5 % of copper — worse than plain steel, because the alloying elements scatter electrons.
iron Conducts electricity A poor conductor for a metal, about a sixth as good as copper, which is why it is a structural material rather than a wiring one.
air Does not conduct An excellent insulator until it is not: at roughly 3 kV per millimetre it ionises and becomes a conductor, which is what a spark and a lightning strike are.
ice Does not conduct A poorer conductor than liquid water, because the ions cannot move through the lattice.
lead Conducts electricity A poor conductor, and heavy, so used for shielding rather than wiring.
tungsten Conducts electricity Moderate, and it is used for its melting point rather than its conductivity.
brass Conducts electricity Moderate. Good enough for electrical fittings where machinability matters more than conductivity.
pine Does not conduct Dry wood is an insulator. Wet wood is not, and it is the moisture that conducts — which is why electricians do not treat a wooden ladder as safe.
silver Conducts electricity The best electrical conductor of any element, better than copper — and too expensive to use for anything but contacts and high-frequency plating.
gray cast iron Conducts electricity Poor electrically, and also a mediocre thermal conductor — cast iron pans are prized for heat capacity rather than conductivity.
diamond Does not conduct An electrical insulator and simultaneously the best thermal conductor known — around five times better than copper at conducting heat while conducting no electricity at all. Structure, not composition, decides both.
high-carbon steel Conducts electricity Poor.
stainless steel 316 Conducts electricity Very poor, marginally worse than 304.
granite Does not conduct An insulator when dry.
aluminum 6061 Conducts electricity Lower than pure aluminium, because alloying always costs conductivity.
soda-lime glass Does not conduct An excellent insulator at room temperature, and a conductor when molten — which is how glass is electrically melted industrially.
PTFE Does not conduct Among the best insulators available, which is why it is the dielectric in high-frequency coaxial cable.
marble Does not conduct An insulator.
unidirectional carbon fibre composite Conducts electricity Conductive along the fibres, which surprises people who assume a composite is plastic. It is why carbon fibre laptop shells need care around electronics and why lightning strike protection is a real design problem on composite aircraft.
rigid PVC Does not conduct A good insulator, and the commonest cable sheathing material in the world.
fibreglass (GRP) Does not conduct An insulator — the reason electricians' ladders and hot-stick tools are fibreglass and not aluminium.
bronze Conducts electricity Modest.
natural rubber Does not conduct A good insulator, and historically the first one used for cable.
paper Does not conduct An insulator when dry, and used as one — oil-impregnated paper insulated high-voltage cable for most of the twentieth century.
mercury Conducts electricity A very poor conductor, and the only metal that is liquid at room temperature — which is what old tilt switches used it for.
aluminum 7075 Conducts electricity Lower again.
tungsten carbide Conducts electricity Conducts, which is what makes it usable as an electrode material.
silicone rubber Does not conduct An insulator, and it retains that property at temperatures where most polymers have failed.
zinc Conducts electricity Adequate, rarely used for conduction.
magnesium Conducts electricity Reasonable, but the metal is used for lightness rather than conduction.
tool steel Conducts electricity Poor.
graphite Conducts electricity The exception among non-metals: graphite conducts because each carbon atom has a spare electron delocalised across the sheet. Diamond, the same element bonded differently, is an insulator.
reinforced concrete Does not conduct The concrete insulates; the reinforcement forms a continuous conductive cage, which is why buildings can use it for earthing.
red oak Does not conduct Insulating when dry.
tin-lead solder (60/40) Conducts electricity Much poorer than the copper it joins, which is why a solder joint is a mechanical and sealing device rather than the conducting path.
platinum Conducts electricity Poor for a precious metal, used for its chemical stability instead.
tin Conducts electricity Poor, and mostly relevant as a solder constituent.
Ti-6Al-4V titanium alloy Conducts electricity About one per cent of copper — among the poorest conductors of any structural metal.
nickel Conducts electricity Modest for a metal.
lead-free solder (SAC305) Conducts electricity Similar to leaded solder and for the same reason unimportant.
chromium Conducts electricity Poor. Chrome plating is for appearance and hardness, not conduction.
silicon carbide Conducts, but only under some conditions A wide-bandgap semiconductor, which is why it is displacing silicon in electric-vehicle power electronics and fast chargers.
leather Does not conduct Insulating when dry.
wrought iron Conducts electricity Poor.
ductile iron Conducts electricity Poor.
Inconel 718 Conducts electricity Very poor.
pewter Conducts electricity Poor.
Monel 400 Conducts electricity Poor.

Common questions

What is the best electrical conductor?
Silver, at about 105 % of copper on the IACS scale. Copper is used instead because silver costs roughly a hundred times more and tarnishes.
Why are power lines aluminium and not copper?
Aluminium is 61 % as conductive by volume but far better by weight. A thicker aluminium conductor carries the same current for much less mass, so the towers can be lighter and further apart — which dominates the cost of a transmission line.
Does pure water conduct electricity?
No. Pure water is an insulator; tap water conducts because of dissolved ions. The electrical hazard from water comes from what is dissolved in it.