Asphalt shingles installed on a roof with a 3 on 12 pitch in an area that has a mean tempreture of 30 degrees in the winter, should have an underlayment of ___?

Asphalt shingles installed on a roof with a 3 on 12 pitch in an area that has a mean tempreture of 30 degrees in the winter, should have an underlayment of ___?