The shape of the helm is another indication of the rank and status of the bearer.

The helms of members of the nobility are open. 
 

The sovereign and princes of the blood - a barred golden helm, affronty.

Peer - a barred silver helm decorated with gold, sideways.

Baronet or knight - a steel helm decorated with silver, visor raised, affronty.

Esquire, gentleman or corporate body - a steel closed helm, sideways.
 

Back cover of French    Red Cross booklet