Do you think the jersey knit bridesmaid dresses are formal?

Alfred Angelo has this kinda new collection of bridesmaid dresses that are made of jersey knit and I thought they might be a good idea. They look comfortable and are reasonably priced for a bridesmaid dress. However my wedding is formal and in the evening, even in a long dress is jersey knit all the formal? I was thinking as saying they could pick of one these 2 dresses a href="http://www.alfredangelo.com/Collections/ProductDisplay.aspx?productID=6c6698da-d583-44ad-a8a3-e28085eee6f2&categoryID=b7a59a7c-2934-461a-9e5f-8478ce891ddf&pg=1" rel="nofollow"http://www.alfredangelo.com/Collections/…/a or a href="http://www.alfredangelo.com/Collections/ProductDisplay.aspx?productID=31315a07-3cc9-47f9-a026-33909ed04b55&categoryID=b7a59a7c-2934-461a-9e5f-8478ce891ddf&pg=1" rel="nofollow"http://www.alfredangelo.com/Collections/…/a but I don't want them under dressed. I know something like this is formal enough a href="http://www.alfredangelo.com/Collections/ProductDisplay.aspx?productID=af0ac9f2-e924-4367-8505-52b60f1bbd3f&categoryID=772f03c9-de43-4942-bfa0-da77e21ebd65&pg=0" rel="nofollow"http://www.alfredangelo.com/Collections/…/a but it is like every other ugly bridesmaid dress.