IST Fathom Blue Apnea Free Diving Spearfishing Fins w/ Flexible Blade & Full Foot Pocket

Quick answer: The IST Fathom Blue is a purpose-built freediving and spearfishing fin with a long, flexible gray blade and a full-foot pocket made of rubber. The largest size is L/XL, which fits men's 12 to 13.

Straight talk on fit

These top out at men's 13. If you're a 13, the L/XL is your size. If you're bigger than that, this fin won't fit you, so head to Fins for Big Feet (Men's US 13 and Up). Full-foot fins are meant to be worn barefoot or with a thin sock. IST suggests its BTA0150 boots, which are like neoprene socks with ultra-thin rubber soles, so you can walk on rocks without ruining the pocket fit.

Why the rubber foot pocket matters

IST chose rubber for the pocket even though it costs more. Rubber lets them build different flexibility and hardness into different parts of the pocket, which plastic compounds can't match. The result is a pocket that gives a spring-like push on each kick while the sole stays rigid and transfers your power to the blade.

The blade

The gray blade is the more flexible option. It's less demanding on your legs and lets you flip through the water quickly, which is a good match for divers who want efficiency over brute power. IST also makes a stiffer blade version.

Specs

• Effective blade size: 22 x 60 cm (8.5 x 24 in)
• Overall length: 92 cm / 36 in (largest size)
• Weight: 3 kg / 6.6 lb per pair on land (largest size)
• Sizes: S/M (men's 8-9), M/L (men's 10-11), L/XL (men's 12-13)

Before you buy

Long freediving fins are a different tool from scuba fins. They're excellent for apnea and spearfishing but long on a crowded boat or in tight spaces. Read How to Choose Scuba Fins for Comfort and Power and Best Scuba Fins for Heavy Legs.