The video starts off with Attoteki Fushinsha no Kiwami showing the materials used for creating the knife: a couple of 100% cotton underwear and briefs made from 92% nylon and 8% polyurethane, SoraNews24 reported.
He then cut the five briefs into strips before pressing with a cast iron pan heated up to about 300 degrees Celsius (572 degrees Fahrenheit).
The nylon-polyurethane materials bind together after being heated, while the cotton remains pliable. He then folds these two types together and heats layer upon layer until it is thick and firm.
After hardening the underwear, the YouTuber then traces a knife on top of the hardened cloth.
He then cuts an outline of the knife off and polishes the sides.
The YouTuber uses sandpaper to make the blade smooth, and a whetstone to sharpen it.
The finished product looks surprisingly like a real knife.
The YouTuber puts the blade to the test by trying to cut several items including meat, paper, and a tough cucumber.
Images via YouTube / kiwami japan