 Other potentially damaging materials include non @-@ archival quality cardboard , card , paper , cotton and cork , all of which give off acidic vapors over time . PVC and polyurethane plastics are also a problem , as they degrade and give off acidic vapors with time . High humidity of the air is a significant contributing factor , as is lack of ventilation of the specimens . High ambient temperatures can increase the rapidity of the decay . 
