They won’t be cashing in their 401Ks or popping Levitra anytime soon, but the brothers Hanson have matured a great deal since their ultra-catchy single “MmmBop” broke out in 1997.

-The rewarding result of this musical puberty is “Underneath,” an album that trades shallow infectiousness for depth and soul, while maintaining the band’s feel-good sound.

The album is the musical equivalent of the NBA Memphis Grizzlies. It lacks one true superstar track, but it goes 13 tracks deep with several songs that grow on you after a second or third listening.

“Strong Enough to Break” opens the album and is, simply put, a heck of a lot of fun. It starts with a nifty acoustic guitar intro and quickly transitions into a typically breezy Hanson tune with a wicked awesome chorus: “Things keep coming and I keep wondering/ I start feeling the walls close in/ Things keep coming and I keep stumbling/ I start feeling strong enough to break.”

The album’s momentum occasionally is stunted by songs that seem too eager to impress. Cuts like “When You’re Gone” and “Believe” are overtly ponderous and dreary. I also had trouble making out lyrics on more than one occasion thanks to some mumbled delivery by the trio that mystifyingly eluded the producers of this otherwise technically flawless disc.

The band fares much better when it lets loose with the high energy “Lost Without Each Other” and “Get Up and Go,” which dares you to try and sit still while listening to it.

Listening to such a sound effort, it’s easy to forget Isaac, Taylor and Zac Hanson are 23, 20 and 18 years old, respectively. If “Underneath” is any indication, Hanson and its music are only going to get better with age.