Being a fibrous product, cores are sensitive to changes in temperature and humidity.  To retain normal dimensions, paper tubes and cores should be used and stored at 73°F and 50% relative humidity (R.H.).  Most problems arise when the relative humidity drastically rises or falls.  Usually these changes take place during the changing of the seasons.  Air conditioned rooms, cold warehouses, low humidity and damp areas all will have an impact on the dimensional stability of fiber cores.  These are the same conditions that cause wooden doors to stick in everyday life.

Cores packaged in cartons – The cores around the outside are the ones most susceptible to change as they are closest to the atmospheric influences.  Cores on the inside of the boxes may not be affected as much because they are more protected.

Snake-laced on pallets; tied in bundles; on racks – Outside perimeter cores are likely to be more affected by drastic humidity and temperature changes, causing inconsistency between different cores.

Wintertime conditions – In severely cold weather when plant heating systems are running for prolonged periods of time, it is likely that the humidity within plants becomes very low.  These are the same conditions in one’s home that cause dry air, sinus problems, doors drying out, static electricity, etc.  These low R.H. conditions usually cause cores to shrink in size due to the evaporation of moisture from the cores.

Summertime conditions – Cores manufactured in high humidity, e.g. 90% R.H., can shrink drastically if the customer puts them into an air conditioned room with extremely low humidity.