We recommend down inserts and source ours from Amazon - full disclosure!  For your convince, we've stocked them for you to include with your order.  Here is the direct link if you'd rather order from Amazon directly, .

Rectangle : 25x15" Feather Insert

Medium : 20" Square Feather Insert (used in our 19" pillow covers)

Large : 26" Square Feather Insert (used in our 22" pillow covers to make them extra full!)