Fibre choice: Why choose wool, cotton, bamboo, acrylic, etc. when crocheting / knitting? Does it make a difference?
Each type of fiber has unique characteristics that must be taken into account when considering substitution (which is pretty much a pattern-by-pattern process). Some examples:

Machine Washability Silk and pure wool arn't machine washable, cotton and most synthetics are, linen is actually improved by being machine washed.

Breathability All of the natural fibers (wool, silk, cotton, linen, etc.) breathe, but the synthetics (acrylic, polyester, etc.) don't.

"Stickiness" Certain techniques (drop stitches, felting) require the built-in self-gripping of wool and similar animal fibers. This also impacts things like cotton's known tendency to droop.

Elasticity This is the fiber's ability to stretch and contract, which affects an item's ability to regain its orignial shape as well as how wearing the yarn is to knit with (hand fatigue). Animal fibers and some synthetics are stretchy, while plant fibers aren't.

Allergies &amp; Sensitivities Wool is the infamous one in both these categories, though synthetics can be problematic, too. Plant fibers do better.

In general, the closer you stick to the recommended fiber type, the more predictable the results will be (replacing cotton with wool is riskier than replacing it with linen). If you really want a specific substitution,  you can try contacting the designer for their thoughts; also, if you're on something like Ravelry, you can see if anybody else has tried it.