Fries can only gain a perfectly crisp crust in oil that's hot enough to rapidly evaporate its external moisture, creating a dehydrated outer layer that's delightfully crunchy.
Vegetable oil which has a high smoke point that ranges between 400 to 450 F is the best oil for french fries because it strikes a balance between affordability and effectiveness.
Vegetable oil's smoke point far exceeds the temperature required to deep-fry most foods, and it's one of the most heat-stable oils that you can pick up at any grocery store.
It’s also pressed from ingredients without strong flavors and goes through a long and thorough refining process that strips away odors, bitterness, and other distracting qualities.
So unlike many oils that have distinct flavors of their own, vegetable oil has a completely neutral flavor that allows the simple, savory, salty taste of french fries to shine.