Which air filter is designed just to protect the furnace from large debris but does not improve air quality?

The air filter designed primarily to protect the furnace from large debris without improving air quality is typically a fiberglass filter. These filters are low-efficiency options that capture larger particles, such as dust and lint, but they do not effectively trap smaller allergens or pollutants like pollen, pet dander, or smoke. Their main purpose is to prevent damage to the heating system rather than enhance indoor air quality.