The two sides of this filter paper are difficult to tell apart. The top side of the filter paper does not have any distinguishable pattern to it. It appears to have irregularities in the material that look like wrinkles in the fibers. The bottom side will show some wrinkles, but there is also a base pattern that looks as if the material has been pressed down onto a fine screen. Depending on how the material has been handled, there may be some creases in the filter paper. These are not the wrinkles mentioned previously. You can tell the difference by the fact that there will be identical marks on the top and bottom at that location. The wrinkled side should be used ‘up’. This is to give the maximum amount of filtration area to the liquid being filtered.