Depends what timescale you mean. Does one cryptocurrency increase 20x in a month? Then yes, it's a bubble, and it will likely crash pretty hard in another mont

Depends what timescale you mean. Does one cryptocurrency increase 20x in a month? Then yes, it's a bubble, and it will likely crash pretty hard in another month or two (but probably not as much as it rose). Does it increase 20x in a few years? Not necessarily a bubble because its value may simply be related to its adoption and potential. The thing about cryptocurrencies is they have rather limited supply once they are launched on the market. So if their userbase/number of adopters increases by 10x overnight, and most of them intend to keep those coins, then it doesn't really qualify as a bubble, even if the value explodes.