An important factor in the properties of NBR is the ratio of acrylonitrile groups to butadiene groups in the polymer backbone, referred to as the ACN content. The lower the ACN content, the lower the glass transition temperature; however, the higher the ACN content, the better resistance the polymer will have to nonpolar solvents as mentioned above.[4] Most applications requiring both solvent resistance and low temperature flexibility require an ACN content of 33%.