Filler boards should be archivally safe. This is the material used behind the backing board or artwork. The filler board acts as a barrier against acid migration and dust, fills space, and adds rigidity to the finished frame package. Various boards can be used: 100% rag boards, acid-free foam boards, or archival corrugated boards. We do not recommend standard corrugated boards because of their acidity.
Dust covers keep dust and insects out and slow the rate of temperature and humidity changes. The traditional method is to cover the back of the frame with kraft paper. The problem with this is that not only is the paper usually very acidic but it inevitably tears and therefore defeats the purpose. We recommend using dust cover tapes. They are available in regular and acid-free versions.