There are 2 types of freight: "Perishables" and "Bulk".
Perishables are electronics, car parts, food, etc. that are carried in containers or specialist vehicles for loose valuable goods or food.
Bulk goods are such loose materials as spoil, gravel, coal, cars, etc. that are carried in open wagons that need no cover (as such).
Of course, the exception to this are "piggyback" or trains like "Le Shuttle" - these are classified, technically, under bulk goods but are normally carried in trains that go at passenger train speeds.