How Kaia Gerber Mastered the Athleisure Uniform: From Birkenstocks to UGG Ultra Minis

Kaia Gerber’s off-duty style has become a blueprint for modern West Coast athleisure, often blending high-fashion accessories with accessible comfort staples.

While she first gained recognition through her mother Cindy Crawford’s lineage, Gerber’s personal aesthetic—specifically her ability to elevate gym wear—stands on its own.

In the spring of 2021, Gerber was frequently spotted navigating Los Angeles in a series of tonal leggings and oversized fleeces, marking a shift toward the “socks-and-sandals” trend that defined the era’s fitness culture.

Between filming commitments for American Horror Story, the model maintained a consistent uniform centered around functionality and ease.

1. Off-Duty Uniform: Birkenstock Arizona Shearling Sandals With Alo Yoga Leggings

On a Saturday in early April, Kaia stepped out for a Pilates class in West Hollywood. She wore Alo Yoga black leggings teamed with a light gray ribbed crop top.

Kaia Gerber nails off-duty athleisure in Alo Yoga leggings and a cozy Free People fleece, finishing the look with socks and shearling-lined Birkenstock Arizona sandals for a relaxed, trend-setting Pilates run on April 3, 2021 (Credit: Instar / WENN)

She layered a Free People “Hit the Slopes” fleece jacket over her activewear and carried a Celine “Ava” bag.

Cindy Crawford’s look-alike daughter pulled her hair back into a messy ponytail and kept a low profile with a pair of tortoise sunglasses and a black face mask.

Kaia Gerber wears a ponytail and styles with tortoiseshell sunglasses, a Celine bag, and a black face mask

To ground her athleisure look, Kaia slipped into black socks and Birkenstock’s “Arizona” shearling sandals—a winterized take on the brand’s iconic two-strap silhouette.

Crafted from velvety suede and lined in plush genuine shearling, the style delivers immediate comfort while retaining Birkenstock’s signature cork-latex footbed and lightweight EVA sole.

Part cozy slipper, part street-style staple, the shearling Arizona has become a defining piece of the modern “socks-and-sandals” formula—effortlessly bridging off-duty ease with a distinctly West Coast, model-approved edge.

Kaia Gerber grounds her off-duty look in black Birkenstock “Arizona” shearling sandals, pairing the plush, fur-lined footbed with socks for a cozy take on the model-approved staple

2. The Socks-and-Sandals Formula: Gymshark Leggings With Fur-Lined Birkenstocks

During the same week, Kaia was seen in another pair of black leggings, this time from Gymshark. She paired her seamless “Vital” leggings with a black “Muse” rib-knit cropped hoodie from Alo Yoga.

The American model completed the outfit with white Set Active socks and her favorite Birkenstock “Arizona” fur sandals.

Kaia Gerber steps out in shearling-lined Birkenstock “Arizona” sandals, pairing the cozy staple with white crew socks, Gymshark leggings, and an Alo Yoga hoodie for a model-off-duty uniform on April 1, 2021

Keeping her accessories simple, Kaia carried a tan Celine “Ava” bag with a Jules Kae vegan-leather hand sanitizer keychain dangling from the strap.

She pulled her hair into a high ponytail and stayed low-key with a pair of oval sunnies and a black face mask.

Kaia Gerber keeps it low-key with a sleek high ponytail, shielding her face behind oval sunglasses and a black mask for an effortlessly cool off-duty moment

3. Cozy Athleisure Done Right: Gray Leggings, Free People Fleece & Birkenstocks

The 2018 British Fashion Awards Model of the Year often relies on a formulaic approach to her fitness wardrobe. On another morning in West Hollywood, she donned a fitted brown low-cut tank top and gray leggings.

Keeping the look cozy, she paired her favorite Free People fleece jacket with thick black socks before slipping into Birkenstock’s fur-lined sandals.

Kaia Gerber teams her Birkenstocks with thick socks, skintight gray leggings, and a Free People fleece jacket on March 30, 2021

With her Celine bag slung over her shoulder, Kaia went bare-faced and tied her short hair back into a ponytail. She then opted for a geeky look with black-framed eyeglasses and stayed safe with a black face mask.

Kaia Gerber keeps her off-duty look grounded in cozy layers, pairing a textured fleece with sleek leggings while shielding her face behind angular glasses and a black mask

4. Elevated Comfort: UGG Ultra Mini Boots With Set Active Lounge Layers

Earlier that spring, Kaia was seen in a color-block sweater from Set Active’s collaboration with Maddie Cline. The crewneck crop sweater features a relaxed fit in soft fleece.

She paired it with Alo Yoga high-waist Alosoft lounge leggings, which utilize a ribbed waistband and velvet-texture fabric.

Kaia Gerber leans into elevated loungewear with a Set Active x Maddie Cline color-block sweater and Alosoft leggings, grounding the look with white crew socks and cozy UGG Classic Ultra Mini boots for a polished yet effortless off-duty moment on March 27, 2021

Wearing her hair in a bun, Kaia shielded her eyes underneath a pair of Oliver Peoples x The Row sunglasses and covered her mouth and nose with a black face mask.

She kept her essentials close with a sleek Celine shoulder bag, casually carrying a pastel Simple Modern Summit water bottle and her iPhone in a playful Wildflower Shrooms case—small details that added personality to her pared-back athleisure look.

Kaia Gerber accessorizes her off-duty look with a curved Celine shoulder bag, pairing it with a pastel Simple Modern Summit water bottle and an iPhone tucked in a playful Wildflower Shrooms case for a subtle mix of polish and personality

To complete her look, Kaia traded her Birks for a cozier pair of UGG Classic Ultra Mini boots—the low-cut silhouette that helped define early-2020s off-duty style and remains a staple in 2026. Sitting right at the ankle with an asymmetrical topline, the Ultra Mini offers a more flattering, leg-lengthening effect than its taller counterparts while making it easier to slip on and off.

Crafted from plush Twinface sheepskin and lined with UGG’s signature UGGplush™ for that cloud-like feel, newer iterations now feature eco-conscious SugarSole™ outsoles made from sugarcane.

Once styled with leggings for a laid-back, model-off-duty uniform, the boot has since evolved into a versatile essential—equally at home with tonal knits, oversized coats, or relaxed denim.

Kaia Gerber finishes her Pilates class look with cozy UGG Classic Ultra Mini boots

Her cozy slip-ons feature a water-repellent Twinface sheepskin upper with sheepskin lining and Treadlite by UGG outsole.

A cute and cozy slip-on bootie with a water-repellent sheepskin upper and UGG Treadlite outsole

Mastering the Off-Duty Aesthetic: Final Thoughts

Kaia Gerber’s ability to turn functional fitness staples into a high-fashion “uniform” is a testament to the enduring power of comfort-first style.

Whether she’s opting for the textured warmth of shearling-lined Birkenstocks or the cozy, ankle-grazing silhouette of UGG Ultra Minis, her footwear choices remain the anchor of her West Coast look. By focusing on quality materials and a consistent color palette, she proves that even the most casual staples can feel intentional and polished.

If you’re looking to replicate Kaia’s effortless vibe or want to ensure your own cozy footwear is the real deal, explore our deeper dives into these iconic brands below.