Field Bandage: Dense Embersilk

Field Bandage: Dense Embersilk is an ability in First Aid. It is an alternate way of making Dense Embersilk Bandages, which normally are made from Embersilk Cloth, by using Heavy Embersilk Bandage as material instead. This ability likely exists because the player will be making a large amount of Heavy Embersilk Bandages to reach First Aid level 525, at which point the ability to make Dense Embersilk Bandage can be learned. With Field Bandage, it is possible to then use all the Heavy bandages to make Dense ones.

Source
Field Bandage is learned from First Aid trainers at First Aid level 525, just like the "regular" ability to create Dense Embersilk Bandages. Both abilities also have the same skillup-potential: 525 → 525 → 530 → 535

Notice that while Field Bandage will make your Heavy Embersilk Bandages a lot more useful, it is still less profitable than making Dense bandages directly from Embersilk Cloth. To make two Heavy bandages you need 4xEmbersilk Cloth, which means making Dense bandages by using Field Bandage is 1xEmbersilk Cloth less profitable.