I don't even understand the question. Do you mean how the plume itself was attached to the helmet on for example a Galea centurion helmet? Or are you asking how horse hairs stand up? Because they do that on their own. Horse hair is very coarse and relatively stiff, it will stand until it starts bending under its own weight. Here's an example, it stands up on its own when cut short and falls when kept long... like human hair.