tomboyx | Premium Underwear for All Day Comfort. Fit for You.

Swim 9" Lined Board Shorts Heavy Weight

Swim 9" Lined Board Shorts Heavy Weight - Main image
$53.72 $79 In stock

Category: swimwear

Reveal an aquatic surprise with our water-activated fabric. When dry, black keeps its secrets hidden. But splash some water on it, and watch as gray jellies emerge.

How It Works

Our innovative color-changing technology responds to water contact. The moment moisture hits the fabric, the previously invisible jellyfish print transforms from black to gray. Once dry, the fabric returns to its sleek, all-black appearance—ready to surprise again and again.

The long inseam swim of dreams. Fitted liner means automatic layering + secure feel. Style these like bike shorts-meet-board-meet-beach.

Sustainability note: We recycle 10-20 water bottles to make each 9" short

  • 9" inseam
  • Drawstring no-roll elastic waist
  • UPF 50
  • Chlorine & saltwater resistant
  • Anti-cling, anti-static, anti-chafe
  • Shell: 90% recycled polyester; 10% spandex
  • Fitted brief lining: 80% recycled polyester; 20% spandex
  • OEKO-TEX® Certified
  • Inclusive sizing from XS-6X
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Standard Shipping: Handling (business days) 0–1; Transit (business days) 7–15.

Express Shipping: Handling (business days) 0–1; Transit (business days) 7–15.

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Standard Shipping · United States: $0.00

Express Shipping · United States: $3.99

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Returning an item

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United States · Return window (days after delivery): 30. Return method: By mail. Return postage: Seller pays.

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Customer Reviews (5.0 / 5 · 5 reviews)

Emily C. ★★★★★

Took these to the beach last weekend and the water-activated jellyfish pattern is genuinely cool — my kids kept splashing me just to watch them appear. The heavy-weight lining feels sturdy without being bulky, and they dried off pretty quick after a swim.

Scarlett A. ★★★★★

I was skeptical about the color-change gimmick, but I’m genuinely impressed—the dry black fabric looks sharp, and the gray jellyfish pattern only shows up once you hit the water, which is a fun surprise. The heavy-weight lining feels sturdy and doesn’t cling, so they’re comfortable for a full day at

Ava C. ★★★★★

The water-activated jellyfish pattern is such a cool party trick—my kids couldn’t stop splashing me to make them appear again. Fabric feels properly thick and lined, no see-through worries even when soaked.