Let's say I have two Commerce Products Types (admin/commerce/products/types), T-Shirts and Hats.

Now, I've a CSV file to import my products into the web store.

SKU;Title;Description;Price;Category;Image
sku_1;This is a T-Shirt;descr_1;1000;category_1;/url/to/image/1.jpg
sku_2;This is a Hat;descr_2;1000;category_2;/url/to/image/2.jpg

In the Settings for Commerce Product processor (admin/structure/feeds/importer_name/settings/FeedsCommerceProductProcessor), Drupal asks me to choose a Product Type.