Heightened competition in the restaurant industry has resulted in a “bun-upmanship” among brands — that is, operators are experimenting with unusual or artisanal sandwich buns to stand out in the crowded sector.

Red Robin Gourmet Burgers, Inc., Greenwood Village, Colo., is introducing the Red Ramen Burger, served on a crispy seasoned ramen bun. The burger, which is topped with teriyaki and Chiu Chow aioli, fried jalapeños and chili-infused shredded cabbage, carrot and onion, will be available through June 5. The product was inspired by the original ramen burger, which rose to Cronut-like fame following its 2013 debut in a Brooklyn food hall.

“We closely follow emerging trends, and when the ramen burger first debuted, our culinary team worked to develop Red Robin’s take on the foodie favorite, enabling us to be the first to offer it nationally,” said Jonathan Muhtar, Red Robin’s senior vice-president and chief marketing officer. “At Red Robin, we strive to constantly provide our guests with unique experiences and menu items that they can’t get anywhere else in the casual dining industry.”

Burger King Corp., Miami, recently unveiled the Angriest Whopper sandwich, sporting a red bun infused with hot sauce. Topped with a spicy sauce, fried onion petals and jalapeños, the burger is a follow-up to the brand’s fall offering, the A.1. Halloween Whopper sandwich, which featured a black bun with A.1. sauce baked in.

“The black bun of our A.1. Halloween Whopper created a lot of conversation and our previous limited-time Angry Whopper sandwich was a hit with guests,” said Axel Schwan, global chief marketing officer for the Burger King brand. “So, we’re combining the power of these past hits into a star-studded sandwich we think our guests will unanimously agree is the next must-eat burger.”

Whereas sandwich innovation centered on creative toppings in recent years, fun buns are now having a moment on mainstream menus, said Aaron Jourden, managing editor with Technomic Inc., a Chicago-based restaurant industry tracker.