Cotton plugs uniformly closes the space while permitting microbe free ventilation. Aluminium foil blocks without ventilation but at times leaves space without filtered air to contaminate

Thank you sir.

yes, permit ari exchange. less 'condensation' formed inside

Also, see the similar question here on RG: https://www.researchgate.net/post/Why_do_we_use_loose-fitting_cotton_plugs_for_bacterial_cultures

I agree the answer from Cyrus:

"a) they allow movement of air into and out of the tube or flask. (b) the meshwork of the cotton fibers acts as an excellent filter preventing entry of fungal spores or bacteria. (c) they are cheap and (d) can be recycled for use in a new batch and re-autoclaved."

Thank you so much sir.

In cotton,non-absorbent (esterified) cotton is used to prevent it from getting wet thereby inviting microbial contamination

Because the cotton is de-esterified in absorbant cotton (solvent treated to remove esters and other particles), it bsorbs water. It is good for bandage and cloth making. Primarily it absorbs moisture thereby keeping the wounds clean. Non-absorbant cotton is raw cotton with oily and fat particles does not abosorb water to basorb moisture and microbe contaminated. Therefore, it is used in tissue culture experiments. Usually handling of abosrbant cotton is preferred due to the soft nature of the cotton facilitating handling.