O'Neill Ninja boots generally follow a conversion where the US size is one size larger than the UK size (e.g., UK 7 = US 8). 

The O'Neill Heat Ninja Split Toe 3mm Boot offers a budget-friendly option for water enthusiasts. Made with a split toe design, this boot provides functionality without unnecessary features. With a thickness of 3mm, it offers the protection and warmth needed for various aquatic activities. Dive in with confidence and comfort.

Fluid Foam
Highly durable neoprene that resists abrasion and compression with a supple feel and good stretch. Stretch factor: 75%

Glued and blindstitched seams

The blindstitch seam is aptly named because the stitching only goes part way through the neoprene. If a boot is blindstitched, it is also glued so there is no leakage through the seams. Glued and blind stitched construction provides a waterproof seam.