Both Reynolds Wrap Heavy Duty and Standard Aluminum Foil have excellent strength and can be used in a variety of situations.
Standard foil does a great job when lining and covering 13"x9" or smaller pans, for wrapping sandwiches and other light items, and for making small packets for oven cooking.
Heavy Duty foil should be used when extra sturdiness is needed. Some examples include lining grills or broiler pans, and for making multiple serving size packets for the grill or oven. This kind of foil also offers extra protection from freezer burn when wrapping foods for freezer storage.