This is not extremely dangerous, but there is a good chance you will get a few very minor burns if you aren't careful. The biggest concern is accidentally starting a fire because burning chunks of cardboard often come loose.
These torches are difficult to extinguish and easy to keep lit. They last 3-10 minutes. If it is smoking, it has a STRONG possibility of self-ignition. To kill it, unravel it or dip it in water.
This will make you smell terrible and put off a lot of smoke.
Step 1: Materials
tape/glue (any tape will work, but masking tape is best for a natural burn in this situation)
lighter and candle
I recommend a wide open environment and a bucket of water.
Step 2: Roll the Cardboard
Leave slightly less than one inch of space in the center, and roll tightly around that. For best results, there should be about 5-7 layers of wrapped cardboard.
Step 3: Secure the Roll
Alternatively, leave a strip of glue in the penultimate wrap and rubber band it until it is dry.
Step 4: Ignite!
The rolled cardboard is difficult to light for the same reason it is difficult to put out.
Here's my method:
Use a wax candle to burn a hole in the top of the inside.
Turn it over and drip melted wax onto the same spot.
Ignite the waxed spot and let it burn the rest of the inside as you slowly turn it, burning the entire interior.
Wait a while until it becomes a sustainable flame and then swing it around to augment air flow.
Alternatively, dip the tip into a liquid accelerant and ignite.