what is the difference between indigestable and undigested?

Indigestible is referred to as the components of food which cannot be digested and absorbed by our body. It is impossible to digest it as body lacks the enzymes required for its digestion. For example, cellulose present in food is indigestible.

Undigestible is referred to as the part is food which can be digested but remains undigested. For example, some part of food remains undigested and is passed onto large intestine.