The Infiniti surf boot is designed for excellent, fast drying warmth and performance. The thinner sole design allows for a better, true-to-the-board feel, and the sole is solid underneath the split toe to prevent annoying leash hangups. The boot is fully lined with Quick Dry Lining, and also features 100% UltraStretch neoprene with a glued & blindstitched seam construction sealed with inner Thermo Dry Seam tape and outer Taitex to keep warmth in. The adjustable Velcro ankle straps allow for a comfortable, snug fit. Even the back ankle pull loop is Pressure Bonded to the outer boot, which keeps even more water out since no stitching ever penetrates through the boot neoprene. Notes: Per the Xcel website, as a guide 5mm boots should be suitable for water temperatures between 8 and 12 °C.  The  Split Toe design is meant to make your foot more stable inside the boot. It stops your foot from sliding around inside the boot, which can cause you to slip when standing up on a surfboard, for example. Downside - some people think the separation feels a bit alien, and as everybody's feet differ, the split toe may not be a good fit for some.    To convert to UK sizing subtract 1 from the US size so a US 6 would be a UK5.