Covering with non-woven fabric and plastic film can maintain temperatures above 8C on cold nights. Check thickness: should be above 0.5mm for adequate insulation. Check materials: quality fabric has high cotton content for better insulation and longer service life. Test by burning: turns to ash indicates high cotton; hard ball indicates chemical fiber. Check breathability by blowing through folded fabric. Multi-layer film alone can keep warm but high humidity causes leaf disease; adding non-woven fabric over inner layer provides better insulation with less condensation.