I bought this pack because they di dnot have the red type in stock and I needed some quickly. One had very thin fabric atspopts; you coul;d see my finger through the thin material. I tried to fit the other one in but the cardboard was too big. It jammed trying to slide it in. Only got one inch inside the furnace frame. Gave up and bought red filters.
3M did not try to help when I sent a message.