On your heavy days (aka days when you use more than two regular tampons) you will probably want to use a menstrual cup or organic tampon as well as your period pants.
However, everybody’s flow is different! The best way to find out is to test the pants and have some spare products in your bag for emergencies.
WUKA holds 20ml of your flow which is equivalent to 4 tampons worth. Luna Undies hold up to 1 tampons worth of blood on their own, or 2 tampons worth with an insert. Some styles of THINX pants hold up to 2 tampons of blood.