Me, the person writting this guide, is not a doctor nor a physician. I'm just very experienced with chest binding (around 7 years old daily binding, tested multiple brands) and want to share my personal advices and warnings. Remember that everyone's body is different, not just in terms on chest sizes but also in physical health, sensory preferences and other forms of difficulties related to chest binding. If I have any written evidences and scientific backups of any of my claim, they'll be hyperlinked within the paragraph which I cited them.
Do not use this guide as medical advice or for moral judgement. Thank you.
Be warned, I explicit talk about breast anatomy and may use terms as "masculinizing". While I don't believe a flat chest is inherently masculine, it is percieved as such by society, therefore someone with a flat chest will be more likely to be percieved as masculine than someone with visible breast.
A chest binder is a piece of underwear that covers one's breast tissue, and compresses it to give it a flatter appearance, by restributing and holding it in place. Unlike sports bras, chest binders were meant for the specific purpose of giving a more masculine appearance to one's chest. Currently speaking, chest binders are the most effective and safest way to flatten one's chest without going through breast reduction and double mastectomy surgeries, while avoiding the dangers of missuing bandages, medical tape and strong sticky tape.
Chest binders were at first design to help cis men with gynomastia (breast growth in males not induced by MTF medical transition), but they're also used a lot by transmasculine individuals, such as transmen, non binary transmasculine people, but also by women who wishes to present themselves in a more masculine way, or cosplayers. Some trans women and detransitionners may also use them during "boy mode" moments.
For today, I will no tackle transtape nor wired (or boned ?) chest binders, all I'm gonna say is that I had pretty bad experiences with transtape.