 Condoms made from sheep intestines , labeled " lambskin " , are also available . Although they are generally effective as a contraceptive by blocking sperm , it is presumed that they are likely less effective than latex in preventing the transmission of agents that cause STDs , because of pores in the material . This is based on the idea that intestines , by their nature , are porous , <unk> membranes , and while sperm are too large to pass through the pores , viruses — such as HIV , herpes , and genital warts — are small enough to pass through . However , there are to date no clinical data confirming or denying this theory . Some believe that lambskin condoms provide a more " natural " sensation , and they lack the <unk> that are inherent to latex , but because of their lesser protection against infection , other <unk> materials such as polyurethane are recommended for latex @-@ allergic users and / or partners . <unk> condoms are also significantly more expensive than other types and as slaughter by @-@ products they are also not vegetarian . 
