Argon is often used to fill their drysuit, because the use of argon allows you to stay warmer during the dive.
Argon has a high insulating effect

Because helium is so poorly insulating due to its high gas density, diving with trimix and a dry suit (fed from the breathing gas) can lead to too much heat loss.
A better option is to add a separate system with which the drysuit can be supplied with gas; an argon bottle with its own machine, which is adjusted to a lower intermediate pressure.
If the water is warm you can also choose to just use compressed air in the argon set.

• Material: L6X aluminum alloy, corrosion-resistant and optimized to improve durability, fracture toughness and resistance to cracking and tearing
• Dimensions: 515 mm length x Ø 111 mm
• Contents: 3 litres
• Weight: ± 5 kilo
• Maximum working pressure: 230 bar
• Cylinder neck thread: M25x2
• CE certificate according to European Pressure Equipment Directive 97/23/EC
• Bottom shape: Flat
• Oxygen clean
• Color: Black matt coating

• Valve, Comptek

• Thread connection: DIN G5/8 female
• Material: Satin chrome plated brass with rubber valve knob