// Only return true if hitting a layer called "MyLayer"

Physics.Raycast(raycast, out hit, range, 1 << LayerMask.NameToLayer("MyLayer"))

// OR

public LayerMask layersToHit; //select in inspector

Physics.Raycast(raycast, out hit, range, layersToHit);

// OR

public LayerMask layersToBypass; //select in inspector

Physics.Raycast(raycast, out hit, range, ~layersToBypass);