Cotton and bamboo require different types and amounts of processing, and you should take this into consideration when choosing cloth diapers that contain these fabrics.
How much processing is required for cotton and bamboo?
Getting the cotton and bamboo off of the plant and into a yarn format takes some processing, but bamboo requires significantly more than cotton.
How is cotton processed?
With cotton, you take the cotton balls off the plant using, I assume, some specialized farming machinery. It’s then cleaned to remove sticks and debris and then is bathed in an alkali solution (caustic soda, also known as lye) to dissolve waxes, hemicellulose, and other junk. It is then 'carded', which means combed out before being spun into yarn. Pretty simple.
How is bamboo processed?
With bamboo, you chop down the bamboo shoots (which are actually a type of grass that grows very quickly). Then you strip it of the bark and other plant-y stuff that it not necessary for textile. (Where all this waste goes and whether it is reused for anything, I have no idea.)
You then cut it up into a little woodchips and run the resulting material through various baths of chemicals. The main chemicals are: 1. Sodium hydroxide (lye), and 2. carbon disulphide. The first is also used in cotton cleaning, and the second is a nerve poison which apparently showed up in high concentration in factory workers but was solved with adequate ventilation. (<-Seems like a suspiciously easy fix...)
From this point, the bamboo is converted into sheets of paper that look like newspaper.
The sheets are dried and stored and then are put through another chemical bath and dried until they're in a fluffy, cottony format. The fluff isn't really bamboo at this point due to all the processing. It is pure cellulose.
Once dry, the fluff is ready to be carded (combed) and spun into yarn the same way cotton is.
Here is a great video on bamboo processing. It leaves out a few steps, but it has some nice visuals to give you a better picture of what's going on.
Is bamboo really bamboo after all the processing?
Because of the amount of processing involved in taking bamboo from shoot to yarn, it ends up that it's not really bamboo any more, but almost pure cellulose. This is why the US Federal Trade Commission (FTC) has said that you're not allowed calling it 'bamboo' and that you must call it 'rayon' or 'viscose'.
There is also some debate as to whether you can even call bamboo a 'natural fibre' given the huge transformation it goes through during processing. My feeling is that it is still natural, since it still has the properties of a natural fibre, namely, breathability, absorbency, and biodegradable. (The fact that bamboo fabric is derived from a natural source is not that convincing to me, since lots of unnatural things are derived from natural sources. For example, polyester and nylon are derived from a natural decomposed organic material---oil--but these fabrics are still not considered natural because of their lack of biodegradability.)
For simplicity, I'll keep calling bamboo fabric 'bamboo' in my blog.
Happy cloth diapering!