If I'm out of adhesive bandage, and have a wound to treat, how can I improvise, using duct tape?
Adhesive bandage is actually a sticky tape with a piece of fabric inside, so I could slice a piece of clothing (I assume, cotton would be preferable?), cover the wound with it, and wrap with a duct tape so that it holds.
What should I take into account when doing such improvised bandage? Are there any dangers of using duct tape, for example, ischemia because it's less flexible than real bandage?
Yes you can. Just be aware that Duct tape is very sticky in comparison to regular medical tape, so when you go to peel it off, it puts a lot more stress on the healing wound and is likely to re-open it.
Ischemia isn't particularly likely unless you are putting pressure on the wound or tightly wrapping all the way around a limb or digit.
One thing that might be of concern is that Duct tape is made in a commercial factory out of substances that haven't been tested for compatibility with human health, whereas medical tape will be made using substances that have been tested for such compatibility. So, you might be more likely to get an allergic reaction to the Duct tape than medical tape, or the Duct tape contains a chemical that inhibits wound healing. Personally I carry a roll of strapping tape (like you use on your ankle when sprained) when hiking for this purpose - it is strong, super sticky, doesn't come off when wet, and works as well as Duct tape for temporary repairs to things like tents.
However, in an emergency, use what you need to and then get professional help!
Given your comment that you want to replace an adhesive bandage, rather than medical tape:
Yes, you can use duct tape + CLEAN cloth for this, but you can do a few things to make it more pleasant.
Note that this is probably not the most efficient improvised bandage that you can make. I would rather improvise with women's sanitary pads than cloth (these make really good improvised bandages and are usually individually wrapped) or glue (you should only use approved non-toxic glue on your skin, but really glue bandages are fantastic).
Re: What type of fabric/material to use... It's less dependent on the fiber content (cotton vs any other type) and more dependent on other properties of the material: clean (very important), not fuzzy/sticking to scabs too much but still being absorbent, being comfortable to the touch, moisture wicking/breathable, and being thin/light enough to tape down.
Natural fibers (cotton, linen, bamboo, wool, silk, etc.) probably get a slight edge up on moisture wicking/breathable, but how the material is created has more impact across the board. Something like a lightweight poly tee shirt would be better than a heavy cotton canvas. (Actually there are studies showing that spider silk is one of the best materials for bandages because it also has some antibacterial properties, but probably most people don't keep large quantities of clean spider silk laying around.)
If you dissect a commercial adhesive bandage you'll notice that they achieve all of this with multiple layers, one layer that prevents it from sticking to scabs and then an inside layer that does all the absorbing, and you can use that technique, too. Also note that I keep saying material instead of fabric. You could make a pretty good bandage with one layer of gauze backed up by a couple of layers of paper towel for absorption.
FWIW, I have found blue Painter's Tape to be preferable to DuctTape for just about any application imaginable. It's strong,lasts, removes easily, etc. Maybe keep a roll of Painter's Tape in your emergency pack instead of DuctTape.
