Invitations--> Tissue inserts or Vellum?

I ordered my wedding invitations (pocket style) online. They shipped without the traditional tissue inserts that prevent ink smudges. According tho the website, they use a smudge free ink so they no longer use the tissues.

It was brought to my attention today that the ink is smudging anyway. So I am going to purchase some inserts.

Question 1- Which type is better for preventing ink smudging? Tissue or Vellum?

My Invites are 4x6, the reception and response cards are slightly smaller but larger than 3x4.

Question 2 - Should I put an insert inside the pocket in between the reception and response cards?

Here is a link to the invites we ordered (gold) http://www.exclusivelyweddings.com/Weddings/Wedding-Invitations/Wedding-Invitation/Best-Sellers/Stylish-Duet-Wedding-Invitation

Thanks in advance!

I'm using Vellum just because the company that did my invitations offers Vellum in the pre-cut sizes. I think Vellum
Would be better for preventing smudges just because it is thicker.