As much as I’m looking forward to summer, this weird period of transitional weather is bumming me out. Right now, for instance, I'm sitting at my desk in shorts, a fleece, and slippers with the window fully open, oscillating between feeling too cold and too hot. Reese Witherspoon apparently also felt this struggle too while on a May walk with fellow A-lister Nicole Kidman as she attempted to stay cool in sporty shorts and a big T-shirt. Kidman, on the other hand, wore a lightweight layer that’s instantly recognizable to just about every activewear lover: The Lululemon Define Jacket.

Currently available in 13 colors, including seasonal tidal teal, mango dream, and ultra-trendy pink flush, this silky smooth zip-up is one piece that’s put the brand on the map. In fact, fellow household names like Kate Middleton, Rita Ora, Jessica Alba, and (fittingly) Reese Witherspoon all have one in their closet. In addition to its smooth, moisture-wicking material, the draw of the Define Jacket is how flattering and functional it is. The sleek shape hugs your sides, contouring to and highlighting your curves. Meanwhile, large front pockets keep your phone and other necessities secure while mesh ventilation panels keep the interior cool and breathable.

Shop now: $118; lululemon.com

In addition to its celebrity fans, the Define Jacket has remained wildly popular for years thanks to rave reviews from fans. It’s “super flattering and comfortable,” wrote one reviewer. “I have five of these and can’t get enough of them,” noted another fan. “I always get a lot of compliments,” they continued, noting that the fit of the jacket gives them a “snatched” look. A third dubbed it a “staple piece of clothing” and a “must have” that they can “throw on with almost anything.”

To be upfront about my bias, I must admit that almost every woman in my family, from my 80-year-old grandmother to my 16-year-old cousin, owns, loves, and wears the Define Jacket on repeat. It gives otherwise basic legging outfits an intentional touch of sleek, sporty, put-togetherness in a way that sweatshirts can’t — just one reason why it’s the pick of royals and A-listers known for their chic style. Shop the workout jacket for $118 at Lululemon.