How to Choose Boys' Swim Trunks: The Complete Guide for Parents

Choosing swim trunks for boys comes down to three things: the right size, the right liner, and the right fabric. Boys' swim trunks should fit comfortably at the waist without requiring constant adjustment, have a liner that provides coverage and prevents chafing, and be made from a fabric that can handle repeated exposure to chlorine, sand, and sunscreen. This guide covers all of it so you can make the right call without second-guessing.

Boy wearing Bermies compression liner swim trunks at the beach with his dad in matching trunks

WHAT TO LOOK FOR IN BOYS' SWIM TRUNKS 👀✍️

1. The Right Fit and Size 📏

Kids grow fast, and swim trunks are one of those things where sizing varies more than you'd expect across brands. A few key guidelines:

  • Go by age and height, not just age. A label that says "8 years" might fit very differently on a small 8-year-old vs. a tall one

  • When in doubt, size up. Swim trunks with an elastic waistband have built-in flexibility, and a slightly larger size will last through more of the season

  • Check the waistband. An adjustable elastic waistband (with a drawstring) is essential for kids, it lets you fine-tune the fit as they grow

  • The length should fall above the knee. Trunks that hit at the knee or below can restrict movement in the water and make swimming harder

Close-up of Bermies boys' swim trunk waistband with elastic and drawstring adjustment

2. Liner Type: Mesh vs. Compression 💪

The liner is one of the most important decisions you'll make, and it's often overlooked.

Mesh liner: the traditional built-in netting that you find in most standard boys' swim trunks. It's lightweight and breathable, but it can bunch up, trap sand, and cause chafing during active use.

Compression liner: a fitted inner short built into the trunk, similar to athletic shorts. It stays in place, eliminates chafing, provides better support during active water play, and doesn't trap sand. Many parents and kids prefer compression liners once they've tried them, especially for kids who are active in the water.

3. Fabric and UV Protection ☀️

Look for:

  • Quick-dry fabric, polyester or nylon blends that dry fast so kids aren't sitting in wet trunks

  • UPF 50+ protection, the fabric blocks 98% of UV rays, providing meaningful sun protection during long beach and pool days

  • Durability, kids are hard on clothing; look for reinforced seams and fabric that can handle repeated washing

At Bermies, all our boys' swim trunks are made from eco-friendly recycled polyester with UPF 50+ protection and a quick-dry nano-coating that sheds water fast. Available in mesh liner and compression liner versions.

SIZING GUIDE FOR BOYS' SWIM TRUNKS

Age (approx.)

Height

Waist

Suggested Size

3–4 years

37–41"

20–21"

XS / 4T

5–6 years

42–47"

21–22"

S / 5–6

7–8 years

48–53"

22–23"

M / 7–8

9–10 years

54–58"

23–25"

L / 9–10

11–12 years

59–63"

25–27"

XL / 11–12

13–14 years

63–67"

27–29"

XXL / 13–14

Note: when in doubt between two sizes, size up. Kids grow, and a slightly larger pair with an adjustable waistband will last longer.

👨👦MATCHING SWIMWEAR FOR FATHER AND SON

One of the most popular reasons parents buy boys' swim trunks from Bermies is for matching father and son swimwear. All of our boys' prints are also available in men's sizes, so you can find the same pattern in both.

The prints are identical, the sizing and cut differ slightly to fit each body type, but the pattern matches perfectly. Great for vacation photos, beach days, and those moments you'll actually want to remember.

Check out our full collection: https://bermies.com/collections/father-and-son-matching-swimwear

Frequently Asked Questions 💡

How should boys' swim trunks fit?

They should sit comfortably at the natural waist, fall above the knee, and allow full freedom of movement. The waistband should be adjustable. If the trunks need to be cinched tight at the waist or fall past the knee, try a different size.

What's better for boys: mesh liner or compression liner?

For active kids who spend a lot of time in the water, a compression liner is better. It stays in place, prevents chafing during running and swimming, and doesn't trap sand. A mesh liner works fine for casual beach days.

Should I size up in boys' swim trunks?

Generally yes, especially if your child is between sizes. An elastic waistband can be tightened with a drawstring, so a slightly larger size will last through more of the season.

Do boys need UPF protection in swim trunks?

Yes. UPF 50+ fabric blocks 98% of UV rays, which is meaningful protection during long days at the beach or pool. It's not a substitute for sunscreen on exposed skin, but it significantly reduces the amount of skin that needs to be covered.

At what age can boys wear compression liner trunks?

Compression liner trunks are suitable for boys of all ages who are active in the water. The liner provides the same benefits for kids as for adults — no chafing, better support, stays in place. Many parents find their kids prefer it over mesh once they've tried it.

 

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