Smart Collections in Shopify allow you full flexibility. These are collections that will contain existing and future products that match the conditions you set will automatically be added to this collection.
Many stores create new smart collections with complex rules just for one purpose: link them to a size chart.
These collections do not need to be visible in your store (!) They are only used for grouping purposes to display a size chart.
Here is an example:
It is very important that collections are not excluded from your Online Store. Else, your size chart won't be visible.
You can hide the collection from your store's navigation. This way, it won't be shown to your customers.