Measure you doorways and windows that you want to leave open to get fresh air.
Go to your hardware store and pick up HVAC Filters. They have various sizes. I used 20 x 25 on the doors and 16x 20 for the windows. You need 2 pieces of wood 1“x 2” x 8 feet per door. Windows I just used the duct tape
Tools you’ll need. Duct tape, scissors, utility knife, tape measure, filters.
Doorway: Cut your wood to the correct size. Lay the wood down and stick the filters in between the 2 pieces of wood. Measure both sides so it is even or your pañal will be crooked. Tape each side length wise first and flip it over and tape. Then tape each individual panel and go around the wood.
You won’t need wood for the windows. Just tape the panels together after measuring.