Plasticine is a good example of a flexible material. All kinds of plastic are also flexible. A common one is PVC used to make many plastic containers.

Note that flexible materials are not elastic, so they will not go back to their original shape, but will stay in any shape you put them. Fabrics are made of flexible yarns – a shirt is a good example. But some fabrics have elastic threads woven into them so they have flexible properties and also elastic ones – socks are a good example.