A flatulence-filtering range of underwear designed to stop farts from smelling has been expanded by British clothing manufacturer Shreddies to include pyjama bottoms and jeans.

Shreddies has extended its range of garments that block gastric odours, having sold over 30,000 pairs of its undergarments since they were launched in 2013.

Like the original boxer shorts and knickers, the pyjama bottoms and jeans include panels made from cloth that incorporates a carbon-based material called Zorflex.

Normally used in chemical warfare suits, the material is capable of stopping smells 200 times stronger than the average fart, however it does nothing to muffle the sound.

The odorous vapours are trapped and neutralised by the carbon, which can be reactivated simply by washing it.

"The technology remains consistent although the design of the carbon within the underwear has changed so that they are more effective," Shreddies manager Richard Woolley told Dezeen.

Based on feedback from underwear wearers, more of the protective material has been added to the longer garments so the carbon lining surrounds the wearer from the waistband down to just above the knee. Shreddies has also amended the design of the underwear.

"We have brought the carbon further up the underwear at the front for both men and women as we noticed there was the potential for odours to escape from this part of the fabric when sitting in certain positions," said Woolley.

The pyjamas are made from cotton and the jeans from denim – both handmade in Leicestershire, England.

Either can be worn with the brand's underwear for double protection, and Shreddies also encourages wearers to go commando in their trousers.

"If you're feeling brave, why not skip the underwear completely!?" said the brand. "You'll never have to worry about those embarrassing moments again."

Although realising that the products cause giggles, the Shreddies team also pointed out that there is a serious side to the project.

"We know fart pants, pyjamas and jeans are funny but we also know we have a product that really helps people with serious medical issues such as irritable bowel syndrome, Crohn's disease, or ulcerative colitis," said the brand.

"People face different situations every day from a business trip to staying at a friend's house or the start of a new relationship, the new garments eliminate odours and worry," added Woolley.

Other designers have been tackling body issues with underwear, including Deborah Dax who incorporated pubic hair panties and a vest designed to look like a dry skin condition into her InConTextUre collection.