Wool tops in different colours can be bough at George Weil or GillianGladRag
2 similar sized pieces of netting (an old net curtain will do)
A water bottle filled with water and a bit of washing up liquid
When you are happy with design add another layer of netting on top. Gently dowse the felt in water and washing up liquid. Now take a smaller piece of bubble wrap and using this rub the felt all over up and down and sideways. Make sure to turn it over and rub the other side too. You will need to do this for a long time. When the design is felted you will be able to peel the netting away without the felt coming apart.
When the felting is done rinse it in water and leave to dry. Now it's your turn! Do post any links of anything you make.