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). 

Crafted from Fluid Foam neoprene, the O'Neill Heat Ninja Split Toe 5/4mm Boot delivers unbeatable value without any unnecessary add-ons. Its supple yet sturdy material offers optimal stretch and durability, while the split toe design and textured rubber sole provide enhanced grip and maneuverability. The glued and blindstitched seams guarantee a waterproof and enduring build.

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.