Pure CO₂
Cheap, deeply penetrating and spattery. It suits structural steel where appearance does not matter and penetration does. The arc is harsher and the bead more heavily crowned, and it is the traditional choice where cost per cubic meter dominates.
Argon/CO₂ mixes
The workshop default. Around 80/20 or 82/18 argon to CO₂ gives a stable arc with much less spatter than pure CO₂, a flatter bead and good penetration. If you buy one bottle for steel MIG, this is it.
Pure argon
For TIG on everything, and for MIG on aluminum. On steel MIG, pure argon gives poor penetration and an unstable arc — it is not a substitute for a mix, and using it that way is a common and expensive mistake.
Flow, not pressure
Set 8 to 12 l/min for MIG with a standard nozzle, less for TIG with a gas lens. Beyond a point more flow becomes turbulent and pulls air in, producing porosity that looks like too little gas — which tempts people to turn it up further.
The questions welders ask
Can I use one bottle for MIG and TIG?
Only if it is pure argon and you accept poor MIG results on steel, or you weld aluminum on both processes. In practice a workshop doing steel MIG and any TIG ends up with an argon/CO₂ mix and a pure argon bottle. Disposable cylinders make that less painful to start with and much more expensive to continue.
How long does a bottle last?
At 10 l/min, a 20-liter bottle filled to 200 bar holds roughly 4,000 liters — about six or seven hours of arc time. Most people are surprised how fast that goes, and equally surprised how much of it is lost to leaks rather than welding. Check every joint with soapy water.
Last reviewed 2026-08-14
