In case anyone is wondering why that doesn't help the OP's issue... In order for the potatoes to be soft on the inside, you have to gelatinize the starch. That means bringing the temperature up to about 60C. However, this results in a gelatin-like block -- no matter how crunchy the outside is. If you want the inside to be fluffy you need to subsequently crystalize the gelatinized starch. You do that by cooling it down. If you've ever eaten cold potatoes or rice, you know how dry it seems -- that's the starch crystals. If you then heat it up again, these crystals re-gelatinize, providing a fluffy interior.

It's often good to go through the cycle more than once, which is why you see recipes for "triple fried" french fries. I tend to like to blanch in salted water, freeze, blanch in oil, freeze and then fry. This also dissolves some of the starch on the outside and provides more surface area for the oil to create crunchy bits. Yeah, it takes all day...

Never been to In-N-Out, so can't comment on what they do.

I worked the fryer at 5 guys and their method is to double fry them. I would drop the fries in for 3 minutes and take them out for 1 then drop them back in again for another minute. Crisps the outside and leaves inside fluffy.

We also soaked the potatoes for several hours to de starch them before frying

Huh interesting to know (as someone who thinks Five Guys makes the 2nd best fries I've ever had, first being a place local to Denver + Colorado Springs)

Other interesting thing about the five guys which you might already know is that their only proprietary ingredient is the buns. The “seasoned” fry seasoning we threw on there was straight up Kroger brand.

Didn't know that actually. Interesting. I knew the flavoring on the base fries was some sort of peanut oil (which is genius, not to mention delicious).

It is straight peanut oil. That was purchased in bulk though from Ben E. Keith IIRC

What's the name of the place in Denver? I always like finding good local places.

Crave. There's one in Highlands Ranch, one in Castle Rock, one at 16th Street Mall.

I'm sure you've read this, but here's further reading for anyone else interested in the science of french fries: http://aht.seriouseats.com/2010/05/the-burger-lab-how-to-mak...

Yes, then they are just stiffer and hotter. Well done is better but not great.

A fry should be crispy on the outside and fluffy on the inside which is not gonna happen with taking a fresh potato and frying it. Freezing and blanching before hand make for better fries.

Part of the problem is that they cut them into shoestring. But another is that they only fry once -- if they did a second fry they'd be far better. I believe McDonalds and other chains pre-cook their fries before they arrive at the restaurant.