/cgl/ - Cosplay & EGL

I'm trying to learn to make patterns in an attempt to improve my cosplay construction, so reading this book on pattern making and I'm trying to order all the things I need.

Most of it's pretty straightforward but I can't figure out what the fuck kind of ruler it wants me to use for this part. At the beginning of the book it lists all the supplies and it mentions a "18 x 2-inch plastic rule (flexible for measuring curves)" so I'm assuming that's what is pictured here but I can't find anything fitting that description online, it seems like a normal plastic ruler would just snap. My first though was just to use measuring tape like the kind you use to take measurements on a person but it says specifically not to.

Does anyone know of a ruler like that or something I can use as an alternative? Would a generic plastic ruler not snap?