Katherine and her mom Nancy Heigl have been cleaning out their closets! The duo are putting some of their favorite designer items up for sale with social shopping platform Poshmark to host a Posh Closet for Charity, listing 85 items to benefit their non-profit animal welfare organization, the Jason Debus Heigl Foundation.

Katherine & Nancy Heigl

Items includes designer brands such as Valentino, Jimmy Choo, Oscar de la Renta, Ralph Lauren, St. John and a Cushnie et Ochs shirt worn by Katherine on a promotional tour for her film Jackie & Ryan.

Speaking to People, Katherine said "I'm incredibly ruthless when it comes to cleaning out. If I haven't worn something for a long time or have never worn it at all, it goes. Of course, now that I'm seeing it all beautifully photographed and up for sale on Poshmark, I'm second guessing my decisions!"

Nancy adds that she had an attachment to some of the pieces because of the special time she spent with her daughter acquiring them: "A lot of these clothes and shoes are from our special mother-daughter shopping days. When we were having a great year and wanted to splurge, we would plan a day at Bergdorf Goodman in New York City and would start out at the top floor, have lunch, and then slowly head down."

Katherine revealed that for her, the hardest items to let go were three pairs of Valentino 'Rockstud' flats, which she can no longer wear after the birth of her son Josh Jr. "I was forced to let go of all my beloved Valentino flats because my feet grew half a size after pregnancy, but I used to wear them all the time!" she says. "They were my go-to shoe for every look and outfit and it still breaks my heart to let them go!"

Katherine Heigl Wearing The Cushnie Et Ochs Shirt Katherine Heigl Wearing The Poshmark Cushnie Et Ochs Shirt

With Mother's Day coming up, the Heigls say that instilling the values of charity and giving back are key to their family life. "For generations, our family has always believed in supporting causes we are passionate about, have always been huge animal lovers, and believe we all need to do whatever we can to improve the world we live in," Nancy said.

Adds Katherine, "I simply lead by example. I include them on days my mother and I are welcoming a new batch of high-risk dogs to our ranch in Utah. We transport the dogs in and are able to shelter and care for them until we find them forever homes. The girls get to meet the dogs and see the work my mother and I are doing. Soon they'll be old enough to volunteer their time to help care for the dogs we've rescued which will not only encourage and support their inherent compassion, but will also be a big help to Nancy and me!"

And there are a few things they're hanging onto for their children, for sentimental purposes; Nancy mentions her own wedding dress, while Katherine says, "I'm keeping my prom dress which I still adore and think is timeless enough one of the girls could wear it to something, though they'll probably disagree! I'm keeping my wedding dress, of course, whether they will want to wear it or not. I'm also keeping a gorgeous custom made gown I wore to present at the Emmys one year – it was made especially for me and I can't bear to part with it."

All proceeds will be donated to support the work of the Heigl Foundation which helps abandoned, neglected and abused companion animals. So if you want to shop in style for Mother's Day and support a great cause, check out the Heigl's closet at Poshmark.