Anyone know how this person does this

so i was looking for how to add 3d armor textures to minecraft and after scrolling for a while i found this yt video https://www.youtube.com/shorts/kJeDtiGqVL0
this is all done using resourcepacks and i needed to know how so i did some searching and found nothing about this project
deos anyone know how he does this. If so please tell me. Im in a bit of a hurry but if you could tell me it will be a great help<:depressive_state:1240465994401579129>