The thin plastic sheet effectively cuts off the flow of room air through the fabric.
( ( The ( thin ( plastic sheet ) ) ) ( effectively ( ( ( ( cuts off ) ( ( the flow ) ( of ( room air ) ) ) ) ( through ( the fabric ) ) ) . ) ) )
(ROOT (S (NP (DT The) (JJ thin) (JJ plastic) (NN sheet)) (ADVP (RB effectively)) (VP (VBZ cuts) (PRT (RP off)) (NP (NP (DT the) (NN flow)) (PP (IN of) (NP (NN room) (NN air)))) (PP (IN through) (NP (DT the) (NN fabric)))) (. .)))
Room air can destroy the fabric if it's not controlled.
( ( Room air ) ( ( can ( ( destroy ( the fabric ) ) ( if ( it ( ( 's not ) controlled ) ) ) ) ) . ) )
(ROOT (S (NP (JJ Room) (NN air)) (VP (MD can) (VP (VB destroy) (NP (DT the) (NN fabric)) (SBAR (IN if) (S (NP (PRP it)) (VP (VBZ 's) (RB not) (VP (VBN controlled))))))) (. .)))