Bursting the Bubble Tulips were the first, but they won’t be the last. What forms a “bubble” and what causes them to burst? Share | Have A Question About This Topic? Name Email Address Question Thank you! Oops! Related Content What Is a Roth 401(k)? Roth 401(k) plans combine features of traditional 401(k) plans with those of a Roth IRA. Mutual Funds vs. ETFs Exchange-traded funds have some things in common with mutual funds, but there are differences, too. Orchestrating Your Retirement Accounts Getting the instruments of your retirement to work in concert may go far in realizing the retirement you imagine.