San Francisco start-up The Flex Company has designed a tampon that allows women to experience "mess-free" sex during their periods.

The Flex tampon aims to help couples become more intimate by allowing them to have sex no matter the time of month.

Shaped like a curved disc, it works in a similar way to the Mooncup, a cup worn inside the vagina during menstruation. Flex fits against the cervix, creating a soft barrier that temporarily blocks menstrual blood.

It is disposable, and can be worn for up to 12 hours – four hours longer than the recommended time for an average tampon.

As it contours to the shape of a woman's cervix, it can't be felt by either partner during sex. But it is not a form of contraception.

"Flex is so shockingly comfortable that women tell us they forget they're on their period while they’re wearing it," CEO Lauren Schulte said during a pitch at Y Combinator's Fellowship Virtual Demo Day.

"We've built a product that allows couples to increase their opportunity to have sex by 23 per cent," she continued. "The great tragedy of people avoiding sex on their period is that this is really the time when women want it most."

According to gynecologist Jane van Dis, Flex has been is hypoallergenic, free of BPA plastic – which is thought to have health implications – and doesn't carry the risk of Toxic Shock Syndrome.

"Flex is a revolutionary device that is changing the way women think about their menstruation," she said in a statement on the company's website. "Unlike other feminine hygiene products, Flex conforms to any woman's body making it the most comfortable product on the market."

Having spent a lot of time embarrassed about her menstrual cycle as a young adult, Schulte developed Flex to "spark positive conversations between men and women about the female body".

The company's mission statement reads: "We believe that a lot of stigma about women's periods is driven by lack of education by men. We don't think men are to blame. Many men have a natural curiosity about the female body, but society teaches us that period talk should be left to women."

"If we can begin educating men and adolescent boys about female anatomy and menstruation in a positive light, knowledge will help shift our ideas – not only about menstruation – but about women."

Flex will initially be available through an online store, where the company are also selling garments featuring abstract diagrams of the female reproductive system.

Customers can preorder from April, with shipping kicking off in September. The company eventually hopes to sell Flex in shops.

Also aiming to solve period problems,  Swedish designer Katarina Hornwall created a necklace pendant that can be used to carry emergency tampons, whilst a device named Loomcup links with a phone app to provide women with information about their menstrual cycle.

Images courtesy of The Flex Company.