Push or Pull thru a flat charcoal filter?

Soon I will be building a filter made like a charcoal sandwich using house ac filters as the 'bread'.

I will be mounting this on a WalMart box fan.

Should the fan pull air through the filter or push the air through the filter?

Push... or Pulll...

Thanks in Advance!

Ideally you want to pull air through a carbon filter.

FYI, DIY

https://www.rollitup.org/do-yourself/154453-d-i-y-box-fan.html#post1976378