Ok so you have the latest must have crazy accurate helmet kit that you just finished building and want to finish the inside to the same standard as the rest of the armour. And if you want your armour to be the closest it can be to the screen used kit then why wouldnt you want the inside of the helmet the same?
When i have shown the inside of my lids before people laugh when you say the interior is 'accurate' they say whats the point of copying something you cannot see? Well apart from being accurate to have the yellow foam cut into a four leaf star shape - its the most comfortable liner ive ever had.
So along side the star shapped foam, you will want to attach an elastic chin strap to where the ears to are screwed in to stop any wobble - and you will want a piece of green lighting lens to complete the interior again held in place by the ear screws.
Screen used examples; the first is ANH and the second ESB, showing even when they reused the original helmets for filming Empire and gave them a refurb they kept the inside to a well known formular..