Maltodextrin is partially broken-down Cornstarch. It is very High-Glycemic. It is used mainly because it gives Bulk without adding alot of weight. There are better choices out there, though. Brown Sugar Twin for example weighs 19g per cup give or take a fraction of a gram, which is 5g less than a cup of Maltodextrin. Granular Splenda is almost entirely Maltodextrin, with a fraction of a gram of Sucralose mixed in.

Weight (grams) per Volume (cup):

Maltodextrin: 24 g/cup
Nonfat Dry Milk: 68 g/cup
Cocoa Powder: 86 g/cup
Dry Whole Milk: 128 g/cup
Cornstarch: 128 g/cup
White Sugar: 192 g/cup
Brown Sugar: 220 g/cup
HFCS: 310 g/cup
Corn Syrup: 328 g/cup