Sharon Simpson, 52, was diagnosed with breast cancer in January 2013. And like many women, the Glasgow resident decided to forego reconstructive surgery after her mastectomy.

Simpson is now cancer-free. But during treatment, she stumbled upon Knitted Knockers—a nonprofit that makes knitted cotton prostheses for women who have lost their breasts to cancer. The organization has been providing free prostheses to women since 2011.

Simpson was so moved by the nonprofit’s mission that she joined a team of “Knockerettes,” volunteers who knit about 300 prostheses each month. “Breast cancer isn’t pink and it isn’t fluffy,” Simpson told BBC News in a video that’s recently gone viral. “It’s a nasty, horrible disease that changes people’s lives…My reason and purpose is to make life better for people in the throes of cancer.”

Why knitted prostheses? Simpson explained they’re lighter-weight and more comfortable than the stick-on silicone breasts offered by the UK’s National Health Service. “It’s quite soft,” Simpson said, holding up a knitted prosthesis. “And it would be natural if that was in a bra.”

The Knockerettes understand there’s no one-size-fits-all approach to prosthetic breasts, so the Knitted Knockers come in a variety of sizes (and colors—from multihued brights to subtle skin tones). Customers can buy prostheses with or without nipples, and they can purchase “aqua knockers” to wear when they go swimming.

“We’ve had feedback from recipients that has made everybody cry,” Simpson said. “We had one lady who hadn’t worn anything other than big baggy t-shirts. And she got her Knitted Knockers, and she went into her wardrobe, and she tried every item of clothing on that she had, because she looked like she did before the mastectomy.”