So far, great! I just put them in and the jury is still out...but they seem to be working well. I have dust and pollen allergies and I live in Arizona. The filters are helping with that.
They say that they are 20x25x4, but they are not in very small print they give you the actual measurement. Our A/C guy did not want to use them because they would allow dirt and dust to get into the unit. Give us what we order.