Passage: Methods of male birth control include condoms, vasectomies and withdrawal. Between 25 and 75% of males who are sexually active would use hormonal birth control if it was available for them. A number of hormonal and non-hormonal methods are in trials, and there is some research looking at the possibility of contraceptive vaccines.A reversible surgical method under investigation is reversible inhibition of sperm under guidance (RISUG) which consists of injecting a polymer gel, styrene maleic anhydride in dimethyl sulfoxide, into the vas deferens. An injection with sodium bicarbonate washes out the substance and restores fertility. Another is an intravas device which involves putting a urethane plug into the vas deferens to block it. A combination of an androgen and a progestin seems promising, as do selective androgen receptor modulators. Ultrasound and methods to heat the testicles have undergone preliminary studies.

Question: A urethane plug is a type of what?
intravas device