Should flax seeds be crushed to be a good egg substitute? When I'm looking up egg substitutes, one of the easiest (for me) is making a slurry of flax seeds and water. However, I noticed there is a difference between using the flax seeds whole and breaking them up. The slurry is thicker if the seeds aren't whole. Or at least, that's what I think I observe.

So, should you only used broken or whole flax seeds, when using them as an egg substitute? Are there (dis)advantages of using flax seeds whole vs. broken up?

I've seen this question, that mentions to break them up, but it isn't specifically about substituting eggs.

Note: I can imagine it also depends if I mind pieces in whatever I'm making, and I don't mind about those.
Yes, for all practical intents and purposes, for flax eggs to congeal they need to be milled or ground to a powder and slurried with water, then introduced to the dish. After stirring and then letting set you should have a nice gloopy mess if you let it stand for a few minutes. 

I typically use a 1 part milled seed to 2.5 parts water, but typically ranges go from 2-3 parts water. You can use a mortar and pestle or coffee grinder for fast, thorough results.


The exception to this is that you can boil them(this link will teach you how to use them to make hair gel, if you're so inclined). This will cause the soluble fiber (the congealing agent) to dissolve, leaving behind the seed husks. Milled flax seeds don't seem to be any less effective and no more distracting in terms of taste so, unless you're doing up your hair, I just don't see the payoff on boiling them.
Another exceptional means to an exception to this is letting the seeds soak for approximately 6-8 hours. As I recall the person who tried this said it didn't congeal much, and was less sticky than a milled flax egg.