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In terms of hobbies, some people cook. Others play sports, while some people knit. And Andrew Gustafson, a math teacher at the Albert Lea Area Learning Center, collects business cards.

He has been doing so since 2016 after hearing about Queen Mary’s College in England making the structures called Menger sponges.

Gustafson described Menger sponges as 3-D fractal shapes that can grow indefinitely and repeat themselves over and over. In theory, these structures could continue on forever.

“I thought it would be a fun way we could talk about math, but it’s also hands-on,” he said. “Kids can make stuff and build something.”

After starting the project at Southwest Middle School, he knew he wanted to continue it after moving to the Area Learning Center. And the best way to do that was by making it an art project.

So after students complete a class with him, he gives them a business card to decorate. After he collects six cards, he’ll make a cube. Some students will contribute one card for one class, while others who take more classes will add more.

“It varies widely, from one to eight or nine,” he said, adding the most he has received from students was between eight and 10.

No tape or staples are added to keep the structure together either.

The cube is a way for students to celebrate the end of a class and student success and acknowledge their accomplishment won’t be forgotten.

Gustafson admitted he doesn’t know what he will do after the sponge gets too big to fit through a classroom door, and he doesn’t know of any practical purpose for the sponge either other than serving as a visual idea of seeing patterns, volume and surface area.

“In math we study fractals to look for patterns and look for repeating, recurring patterns,” he said. “But I think as a structure in and of itself, it just is.”

Regardless, the cube won’t go away either, and students have the opportunity to return after they’ve left to see their work.

The cube is also related to the subjects of volume, surface area and infinity, a concept that intrigued him, noting if the sponge grew forever it would have an infinite surface area with zero volume.

When students ask how many cards there were, he’ll ask them informally to find out how many cards are on each face and the number of faces that were covered.

He said student reaction to the project was positive, noting he hadn’t encountered a student who didn’t participate.

Samuel Reyes, a former student of Gustafson’s who contributed eight cards, first heard about it last year.

“At first I didn’t know what to think,” he said. “But then he talked to me about it, showed me a little bit, and I thought it was pretty cool about how big it’s really going to get and how small it is now.”

By Gustafson’s estimation, hundreds of students from his time at the middle school and the learning center have participated.

After using over 17,000 cards already, he isn’t halfway to his goal of having the 50,000 cards necessary to complete the Menger sponge, a project he estimated would take nine more years in total to finish.

“I only build as students earn credits,” he said. “… I don’t know how fast or how slow they’re going to earn credits, so I can’t say when [it will be completed].”

It takes six business cards to make one box, and he said he is running out of business cards.

“I want to continue this project over the next however many years I can,” he said.

While he appreciates the donations he has received, he is now looking for any old business cards anyone may have, whether the company changed logos or title, name, address or anything else. And he’d love to use them if someone else wasn’t.

If anyone has business cards they would like to donate, reach out to Gustafson through email at andrew.gustafson@alschools.org. Texture and color of the cards does not matter. Business cards are generally 9 centimeters by 5 centimeters.

Reyes has already informed Gustafson he’ll come back after the sponge is complete.