When you lose the bobble off the top of your favourite hat, replace it with a new one instead of throwing it out. Making bobbles at home gives you the freedom to add colour and style to an old hat without having to spend the money to buy a new one. A bobble can also add the final touch to a homemade winter cap. With a few basic supplies, you can make a new bobble to fit a knitted hat.
Lay the cardboard on a flat surface. Place the round object on top of the cardboard. The round object should be as large in diameter as you would like the bobble to be. Choose a glass, can or jar as the round object.
Trace the round object onto the cardboard twice, creating two equal circles. Cut out both circles. Cut a slit into the side of each circle, directly into the centre.
Use the slit to position the scissors into the centre of the cardboard circle. Cut a smaller circle out of the centre of each circle. The cardboard pieces will be ring-shaped with a slit in each side. Cut through each circle, about 3.5 cm (1 inch) away from the slit to remove a small piece of cardboard. The pieces will look like a ring, with a 2.5 cm (1 inch) piece removed from the side.
Cut a piece of yarn from the skein. It should be long enough to lie on top of one of the rings. The yarn will sit between the two rings and loop around, following the shape of the cardboard. Leave about a 30 cm (12 inch) tail.
Lay one cardboard ring on a flat surface. Lay the piece of yarn on top of the cardboard. Loop the yarn so that it lies entirely on the cardboard, following the ring shape. At the opening in the cardboard ring, pull the yarn so that the two ends hang out. Each end should measure about 15 cm (6 inches).
Place the second piece of cardboard over the yarn. The only yarn you should be able to see are the 15 cm (6 inches) tails hanging out of the bottom.
Pull the loose end from the skein. Start in the middle of the ring, directly across from the cut-out piece and wrap it around both cardboard pieces. This will secure the yarn piece between the cardboard into place.
Wrap the yarn around the cardboard pieces. Work toward the right, wrapping the yarn close together. When you reach the end of the cardboard, continue wrapping the yarn back toward the middle, where you started.
Wrap the yarn past the middle and work toward the left end of the cardboard rings. When you reach the end of the cardboard, continue wrapping back toward the middle. If you would like your bobble to appear thick and full, add another layer of yarn to the cardboard rings.
Cut the end of yarn from the skein. Be careful that the yarn does not unravel from the cardboard. Pull the tails of the yarn in between the cardboard and tie a loose slipknot.
Slide the scissors in between the outside edges of the two cardboard rings. Cut the yarn that is wrapped around the circles.
Pull the yarn tails tightly together. As you pull, the yarn that was wrapped around the cardboard will draw in, creating a bobble. Tie a tight knot on the yarn tails to hold them together. Remove the cardboard rings.
Sew the bobble to the knitted hat with the yarn tails and a large needle.