Get a set of detailed drawn instructions to use this Adjustable Elastic Breathable Waist Band system on any of your projects.
Along with it you will get access to a private online whiteboard (on Miro), where more nerdy details can be found and where you can leave comments with questions about any step, which I'll personally answer to.
 
In short what is great about this system:
Adjustable - giving 12 cm between minimum and maximum waist measurements of the garment;
Elastic - allows the garment to be pulled on and off;
Breathable - it uses elastic cords instead of flat band elastic, which leads to superior breathability and faster drying time;
Plus additional feature of this system is that the elastic cord can be easily replaced, when worn out, with no sewing required. See repair instructions here, under 'waist belt shortening' - https://www.functionalclothinglab.com/12032-pants-instructions
 
Read an Intro - https://www.functionalclothinglab.com/post/aebwb-part1 - it talks in details about what led to the development of the system and the logic behind the design choices.
Then read a Second part talking more about technical details of the system - https://www.functionalclothinglab.com/post/aebwb-part2
Though most nitpicky details can be only found on the online board, which you can get access to by purchasing this set of instructions ;)