The Steel Door Institute (SDI) was established in 1954 as a voluntary, unincorporated, non-profit business association whose mission is to promote the use of steel doors and frames in the construction industry. Membership is open to all American based companies engaged in the production for sale of swing steel doors and/or frames on a national basis for at least two years. Members mutually agree to establish and abide by SDI manufacturing and quality standards that apply to all doors and frames they produce.