How does the product type filtering work?

Shopify allows assigning a product type to each product. This can be done on the Shopify product editing page:

You can limit the random recommendations displayed to products of the same type of the current product. Just go to the Recommendation Tuning section and click on the Configure random recommendations button:

Select the Filter by product type option (random recommendations must be enabled as shown in the previous screenshot):

Let's say, for example, that you're seeing a product page whose product type is Shirts. The random recommendations displayed will only be products with product type Shirts.

Please note that, if there are not enough products matching the selected criteria, the recommendations will be automatically completed using random recommendations.