Corrugated cardboard is the prototyping material: free, available everywhere, it lets you validate a cut before committing plywood. It is also the most fire-prone.
Settings: what really matters
Corrugated board is not a solid material: the beam crosses two liners and a void. The cut is therefore uneven if speed is too high — the void lets the beam diverge and the bottom liner stays attached in places.
One pass at moderate power and medium speed works better than two fast passes, which re-cut the same line and widen the burn.
For a jig prototype, double-wall board behaves almost like 5 mm solid: an excellent test of your paths, not of your settings.
Risks and finishing
This is the material that catches fire fastest, and the flame travels inside the flute where you cannot see it. The rule is absolute: never unattended, extinguisher within reach, and inspect the piece before closing the machine.
Printed or laminated board (food packaging, glossy boxes) contains unknown inks and films: prefer plain brown board.
The edge stays brown and dusty, which does not matter for a prototype. For a visible final piece, solid grey board (bookbinding board) gives a much cleaner edge.
Every figure on LaserSettings comes with the machine, the laser source, the material and the thickness it was tested on. A setting published for a 10 W diode says nothing about a 40 W CO2, and a setting for 3 mm says nothing about 6 mm: check those four things before you copy any number.
Settings are confirmed or disputed by the members who reproduce them, so reliability comes from cross-checking rather than popularity. Photos of the result — cut edges, engraving shades, scorching — tell you more than a single number found on a forum.
Whatever the material, treat a published setting as a starting point: run a small power/speed test grid on an offcut, clean the lens, redo the focus, work with fume extraction and air assist, wear glasses rated for your wavelength and never leave the machine unattended.