Shoe brand Crocs Inc. (CROX) has seen a huge boost in popularity in 2021.

To some, the foam plastic footwear is ideal to wear when nobody is around, while others consider it a trendy fashion statement.

The Colorado-based company reported a second-quarter sales surge of 93.3%. The company reported that profits gained 166% in the past year with U.S. sales up 135.8%.

Crocs was founded in 2002 and are known for their hole-covered clogs. The shoes are relatively inexpensive. On the company's website, the most expensive women's Crocs cost $79.99 and the least expensive cost $17.49.

But how have these unique shoes become so popular in 2021? CEO Andrew Rees on Monday explained the surge in attention.

"It's comfortable [the shoes], it's easy on and off. It's lightweight, so it's very easy to wear and it appeals to that major comfort trend that is going on. Number two, we add a great deal of excitement and inspiration to the brand through the collaborations. And then I think thirdly is the international nature of the brand. We are already in 19 countries around the world, and so we penetrate into those markets," Rees explained to Brian Sozzi on Yahoo Finance Live.

Crocs also did a marketing revamp. Brand collaborations became one of Crocs's most recognizable marketing moves by adding a fun stylish touch to these partnerships. Crocs have partnered with multiple different known brands and people, some include Justin Bieber, Vera Bradley, The Movie “Cars”, KFC, and Balenciaga.

In May, the Wall Street Journal noted how Crocs stuck with what it was good at: "easy-to-clean, easy-on-easy-off, comfortable, colorful" shoes. The Journal noted how Crocs closed some stores and sold to online retailers like Amazon, Tmall and others.

Crocs, which has a market capitalization of $8.5 billion, has seen a surge in its share price.

Shares of Crocs were trading at $35.90 on July 27, 2020. As of 1:49 p.m. ET on Monday, shares of Crocs were trading at $130.76, down $0.53, or 0.40%.