Heterosexuality is one of the fastest growing sexual behaviors:

They love the flavor of the rainbow.

We’re more than half a century into the sexual revolution—people continue to explore the spectrum of their sexual orientation beyond being gay, straight, or bisexual,

Since then, a niche but increasingly mainstream part of the gender spectrum has emerged: heteroflexibility. According to Verywell Mind, not to be confused with bisexuality, in which people are equally attracted to men and women, heterosexuals primarily identify themselves as heterosexual, but sometimes engage in orgies with members.

Feeld, a dating app looking for alternative relationship structures, recently released its annual Raw Report, which provides insights into the preferences shaping contemporary intimacy. Survey results show that heterosexual flexibility is the fastest growing sexual practice in the UK, with the number of practitioners soaring 193% from last year.

At the same time, it is estimated that a staggering 15% of the U.S. population, or approximately 50 to 55 million Americans, now consider themselves heterogeneous.

“We’re seeing more and more people exploring connection and entertainment in authentic, fluid ways, redefining what it means to be seen and connected in 2025,” said Dina Mohammad-Laity, vice president of data at Feld.

Among the heteroflexibles, two-thirds are Millennials (those born between the early 1980s and 1996), 18% are Generation Z (those born between 1997 and 2012), and 15.5% are Generation X (those born between 1965 and 1980).

Meanwhile, Berlin is the most heterosexually flexible city in the world, while New York City has the fastest-growing bisexual population, up 161%, according to research.

Perhaps a caveat for sex experts is that the term is somewhat subjective and, for lack of a better word, flexible.

For example, this category covers a variety of people, including people who are heterosexual but prefer to be with people of the same sex, heterosexuals who occasionally feel same-sex attraction, and people who are curious about bisexuality.

It can even work for women who are in a relationship with one man but are open to a threesome involving another woman.

In fact, some accuse heterosexuals of encroaching on bisexual and pansexual territory and even causing their disappearance.

Dr Luke Brenning, a lecturer in applied ethics at the University of Leeds in the UK, explained that the evolving identities illuminated by this study “show an increasing awareness that sexuality is complex”.

“If anything, it would be surprising if people were never sexually curious about people of their own gender or gender, or if attraction worked in a neat and predictable way,” he said.