NURBS (Non-Uniform Rational B-Spline) curves can be used to create surfaces that are stored as mathemematical definitions rather than as polygons. Not only do they make it possible to store objects with complex curved surfaces very efficiently (ie very small file size) but they also allow the renderer to draw the surface beautifully at any distance. The renderer tesselates the surface dynamically so that the number of polygons used to render it at any distance is sufficient for the curve to look good and run efficiently.

NURBS are supported as an extension to VRML97 by Blaxxun Contact, ParallelGraphics Cortona, and some other VRML browsers. Some 3D modelling packages give you the option to export curved surfaces as NURBS surfaces or to convert them into indexed face sets. While NURBS are more efficient and look nicer, indexed face sets offer better compatibility across VRML viewers.

There is currently a trend in 3D modelling packages from working primarily with polygons to working with curved surfaces, however most packages support both ways of modelling and enable polygon and NURBS surfaces to be used together to create objects].