Can cardboard be used for an airtight seal?

Guys, I have an 8 inch fan attached to a Wye connector in order to split my ducting for two rows of lights. Currently only one row is being used, so I covered one end of the Wye with a circular piece of cardboard and secured it with aluminum duct tape as a seal.

Only thing I'm concerned about is that my fan might be so strong that it might pull air right through the cardboard (if the cardboard is porous enough) the cardboard itself is smooth and free of creases or any kind of damage, but I'm not certain if it can hold out the air. What do you guys think?

If it isn't water tight, it isn't air tight, but I think you'll be fine. Personally I wouldn't grow in a cardboard box, good way to start a fire. If your fan was powerful enough to pull air through the cardboard, it would probably collapse on itself. As long as there is a dedicated airflow path it won't be an issue.

It's not air tight.
It's cardboard.

Build a wooden box.

It's not airtight and it's fire hazard. Buy some good 2x3 or 2x4 and fireproof drywall, cheap and safe way to build grow rooms.

can anyone help i have a plant in 1st week of flowering and is nute loocked its leaves are curling,turningyellow and is turning purple on da edges slightly the ph has not moved in a week i flushed with fresh water cleaned da bucket and still nuthing refilled with fresh nuted also. was growing perfect until now .should i take out all nitrogen already.any advice on how to unlock this beauty is very much appreciated.smoke big

Nute locks plants usually takes about a full week to recover if not severly burnt, Water only few days and back off to half strenght.