Ski boots and sole norms: the standards that make boot and binding fit together.

Alpine boots: ISO 5355

ISO 5355:2019, "Alpine ski-boots: Requirements and test methods", is edition 5, published in April 2019, and is the current edition in the ISO catalogue as found. Its catalogue scope covers alpine boots in the Mondopoint sizing system from size 15.0, in two types: A for adults and C for children. A sixth edition was at committee-draft stage (ISO/CD 5355) when the research searched, which is unconfirmed beyond the listing.

The earlier editions are all withdrawn:

• 2005, with a 2007 corrigendum;
• 1997 and 1991, both titled "Safety requirements and test methods";
• 1982, titled "Ski boots for adults: Interfaces for ski bindings for downhill skiing".

FIS defines the alpine racing boot by reference to ISO 5355 (alpine specifications 2026/27, rule 3.2.1).

Touring boots: ISO 9523

ISO 9523:2023, "Touring ski-boots for adults: Interface with touring ski-bindings: Requirements and test methods", is edition 5, from December 2023. Its catalogue scope is rigid-soled touring boots that attach at toe and heel, and it excludes boots with softer shells, such as telemark boots. The 1990, 2008, 2015 and 2019 editions are withdrawn.

Alpine boots with walking soles: ISO 23223

ISO 23223:2025, "Alpine ski boots with improved walking soles: Interface with alpine ski-bindings: Requirements, test methods and marking", is edition 2, from February 2025. It replaced edition 1 of 2021. Its stated aim, in the catalogue entry, is better walking without affecting the function of alpine bindings designed for such soles.

GripWalk, and which norm it falls under

GripWalk is a boot-sole and binding system credited to Marker and Dalbello (MDV Sports) and first shown at ISPO in 2016. A Snowsports News report of August 2021 said ISO 23223 now defines the sole shape for boots with improved walking function, alongside ISO 5355 and ISO 9523. The same report said ISO 23223 takes full effect for products developed for the 2022/23 season onward; that rests on one trade report relaying the maker and is unconfirmed. The report also relays a claim by MDV Sports that more than 20 companies license GripWalk and that over 60 percent of alpine boots and bindings for 2020/21 already had it or were compatible with it.

The sources disagree about which standard GripWalk sits under:

• Snowsports News (2021): GripWalk falls under ISO 23223.
• A retailer's compatibility guide (seen only as a search summary): GripWalk soles meet ISO 9523. The same guide says another walking-sole system, Walk To Ride (WTR), is not defined by an international standard, while also saying WTR soles meet ISO 9523, so the guide contradicts itself.

This site follows the ISO 23223 account, as the research behind it recommends, and gives the retailer's version only as the other side. The makers' own compatibility lists are where each boot and binding pairing is stated.

Flex numbers

Boot flex numbers are set by each manufacturer. A June 2011 article on Wildsnow, a backcountry-skiing publication, by Louis Dawson says no official flex standard exists, that the informal scale runs roughly from 30 to 130, and that the numbers mainly rank models within one brand. The article also says boot stiffness changes with the temperature of the plastic. Salomon, a maker, is reported in a search-result summary (its page could not be opened, so the wording is unconfirmed) as saying that boots with the same flex rating can differ between brands and categories, and that stiffness depends on shell material and thickness, buckles and liner.

Boots in the racing rules

The alpine stand-height limit, which works together with the boot-sole limit, is on FIS race ski rules. Snowboard boots appear in the research only through the binding standards, on bindings and standards.