Measure and cut out 4x4 in (101.6x101.6 mm) squares on your white felt. Draw a grid on your 18x18 inch (457.2x457.2 mm) sheet of white felt to create smaller 4x4 inch (101.6x101.6 mm) squares. If you measure properly and don't waste the felt, you can create 20 4x4 inch (101.6x101.6 mm) squares out of a single piece of 18x18 inch (457.2x457.2 mm) felt. After you've marked the lines with a pen or marker, proceed to cut the felt into squares.
Cut two 2x8 inch (50.8x203.2 mm) strips from your multicolored felt. Take your seven sheets of multicolored felt and create two 2x8 inch (50.8x203.2 mm) strips per color. You'll continue to cut these strips of felt to add as decorations over your 4x4 inch (101.6x101.6 mm) white square.
* You can buy multicolored felt in bundles at most craft stores or on online boutiques like Etsy
Cut eight two inch (50.8 mm) squares per piece of felt from your strips. From each strip of felt, you should be able to cut out four 2x2 inch (50.8x50.8 mm) squares of different colored felts. These squares should be 1/4 the size of your 4x4 inch (101.6x101.6 mm) piece of white felt. These will act as your modular pieces or the pieces of felt that will lay over your 4x4 inch (101.6x101.6 mm) white squares.
Snip squares of colored felt in half, diagonally. This will create six triangles and will make your coasters look different and break up the shapes on their surface. Cut the triangles so that you end up with right triangles.
Pin your modular pieces onto your 4x4 inch (101.6x101.6 mm) squares. Get creative and lay your multicolored pieces over your white felt. Arrange the felt so that the surfaces of your felt coasters look unique and colorful. Use the smaller pieces in each corner of your coaster to create different designs.
* For example, you can have a pink triangle in the upper left, a blue square in the lower left, a red square in the upper right, and an orange triangle in the lower right.
Sew along the inner edges of your modular pieces. Once you're happy with the arrangement of your pieces, you can start to sew along the inner edges. Cut 18 inches (457.2 mm) of your cotton thread and thread it through the eye of your embroidery needle. Pierce the modular pieces and the white 4x4 inch (101.6x101.6 mm) square in order to hold them in place. For this step, you'll only need to sew the inner edges.
Turn your coaster over and stitch along the edge of the coaster. Instead of having to sew each modular piece all the way around, you can take a shortcut by turning the coaster over and sewing along the edge of the coaster. This will finish holding your modular pieces in place and will complete your project. After sewing, simply turn your coaster over and use it.
* Cut a 24 inch (609.6 mm) thread for this portion of the project.
Done! You can now use your modular felt coasters.