In Sydney or Seattle nobody would bat an eyelid, but the couples are part of a thriving underground swinging scene that is an anomaly for a country where oral sex is illegal and Playboy magazine is banned.
There are more than 10 swingers clubs in Singapore, most of them private, some of them online. With more than 6,000 members, the Web-based United SG Swingers is one of the biggest.
"There are a lot more people that are open to the idea. It's so widespread now," said a 42-year-old Singaporean company executive who only wanted to be identified as Jack.
"Swinging is all about sex. It's satisfying the urge to have casual sex and doing it with somebody you're comfortable with," said Jack, who has been swinging for 10 years.
For all their enthusiasm, few swingers tell family and friends about their lifestyle, although the practice is not illegal in Singapore.
"In Singapore, most people will perceive us as perverts," said a 39-year-old publisher who has been swinging for five years. "Look at our government policies, they say: 'Let's open up.' But our policies have always remained very conservative."
Wealthy Singapore, which has consistently ranked near the bottom in a global survey of sexually active nations, has been struggling to shake off its reputation for prudishness.
On Friday, it opened Sexpo 2006, the country's second sex exhibition, featuring an array of toys and seminars.
At United SG Swingers, people share erotic photographs, exchange personal ads and correspond about the next gathering. It is a close-knit community in which couples recommend good sex partners and criticise those who aren't.
A police spokesman confirmed that swinging is not illegal as long as it is done behind closed doors, is consensual and no money changes hands.
This year, the organisers of United SG Swingers started holding "on premise" parties, where couples can engage in group sex in houses and hotel rooms across Singapore.
At these parties, the bedrooms have a strict clothes-off rule and the "hard swingers" can engage in partner swapping. The "soft swingers" are couples who stand around and watch, or have sex with their own partners in full view of others.
Couples who swing say that seeing their own partners in action keeps their passion burning.
"It's like looking at cake and wanting to eat it," said the main organiser of United SG Swingers, 37-year-old IT specialist Josh, as his 32-year-old wife nodded in agreement.
But some swingers disapprove of these parties, saying they can degenerate into orgies.
"You can't establish pure friendships when there's a large group," said Ishak. "Genuine swingers would want to establish trust -- you can't trust a person just by meeting them one time and then think they can do it with your wife."
A 34-year-old Australian who attends swinging parties told Reuters that Singapore's scene is just evolving.
"It's very innocuous here, it's not like other countries," he said. "Compared to Australia and Europe, it's more discreet and less lively. Singaporeans are pretty reserved in a lot of ways."