Straight is the new black for frizzy-haired bar-goers, who can now flatten their wild locks between beers.

Nearly 20 pubs and bars across the country are offering hair straighteners in the women's toilets, giving patrons the offer to straighten their hair for two minutes, at $2 a pop.

Newmarket's Mac's Brewbar was among the first to install the hair straighteners, already hugely popular in Irish and Australian bars.

Shawn Brookes, co-owner of Mac's, said the straighteners had proved "extremely" popular with the ladies.

The machines were put in during a recent refit of the bar in an effort to make it more female friendly.

"The other day a woman came in who obviously had a big Friday night and was running late for work on Saturday and didn't have time to straighten her hair," said Brookes. "She asked for change for a $2 coin so she could use the machine. I had a bit of chuckle over that."

Brookes said the machine has so far given them about $80 and it's used between 10 and 12 times a week.

"It's still catching on but we've had really good feedback on it.

"We've got to keep up with the fashions. Straight hair is still in it would be good if they put out a curling iron as well though."

Toni Robinson, of Red Shoelace, the company licensed to install the GHD hair straightener vending machines, said the idea was taking off in bars, restaurants and even backpackers' accommodation around the country.

"We've just had one installed at a backpackers in Queenstown and it's really taken off."