Tensile, they're strong as hell if you look after them. If I were you I'd clean it out when it's brand new, they come packed full of grease and it sticks the springs together and makes it skip when new, which is why people think that they have to "bed in". (It's a freewheel, theres nothing to bed in...) I used to just run mine with WD40 in it, lasted me 2 years and 4 months and was still never skipping when I sold the bike!