Why does adding commercial processed cheese to fondue change its consistency? I like to experiment with cheese fondues.  I've had good results with the traditional Emmentaler and Gruyère mixture, but the best result I've had was when I added some cheese from the supermarket that was labeled as a "Cheddar Blend".  I'm not entirely sure what that means, but it resulted in a fondue that had a wonderful creamy consistency, which very quickly settled into a nice even coating when lifting out the dipped items.  It didn't add a huge amount of flavour on its own, but it helped to carry the stronger flavour cheeses, which I've often had trouble getting into a good consistency on their own (they often either wind up too thin [leading to soggy wine-flavoured bread] or a bit grainy from the flour or cornstarch I try to use to thicken it a bit.)

My question, then, is what is it about this 'Blend' cheese that improved the consistency of the fondue?  I imagine it's something they add to make it a blend in the first place.
The magic is from Sodium Citrate

Most mass produced cheese it based on "cheddar blends". Basically large (50 Kg to 1 Mg) blocks of cheese are made in a milk factory. When a consumer product is to be made from it, the cheddar is shredded, flavour and/or culture is added, and then using heat and pressure it is re-packed into consumer sized packages

In some cases Sodium Citrate is added to improve the hold-together of the cheese

Sodium Citrate is an old additive for "cooking cheese", and it can be made at home with baking soda and lemon juice. Gently heat the juice of half a lemon in a microwave safe bowl, then add 1/2 to 1 tsp of baking soda and heat until fully reacted (bubbles cease). Add about a cup of grated cheese (hard or soft) and repeat a gentle heat and stir cycle until it forms a smooth "sauce"

This will remain liquid while warm

If you let this cool you can mold it, or form "slices"

http://modernistcuisine.com/recipes/silky-smooth-macaroni-and-cheese