Almost every kid I've ever known as gotten more excited about the box a gift came in than the gift inside, but this blanket is sure to be an exception. Composed of foam and felt, this blanket's grid of triangles not only offers a way to learn about geometry, but also to let your imagination run wild!

Unlike standard blankets that just let you snuggle up and keep warm (which it also does), this one can also be used to teach kids the Pythagorean theorem (a²+b²=c²) or the angle sum of triangles (the three angles of a triangle added together always equal 180^o). You could also use it for simpler concepts like addition or simple counting, or to make an awesome fort!

Learning Objectives
Learning Objective 1: By constructing this blanket, students will be able to master simple math (counting, addition, division, etc.)
Example 1: Counting the triangles and squares in one row and determining how many compose the entire blanket
Example 2: Dividing the length of each side of the blanket by 6" to determine how many squares should be in each column and row

Learning Objective 2: By constructing this blanket, students will be able to enhance their understanding of simple geometry
Example: The division of a square into rectangular rows and columns, and those rows and columns into squares, and those squares into triangles. Numerous shapes can be plotted out on the completed blanket, and 3D shapes can be constructed using the blanket to explore surface area and volume

Learning Objective 3: By constructing this blanket, students will be able to explore the angle sum of triangles
Example: The blanket offers a clear, visual representation of how the angles of triangles add to 180^o. Further, a protractor can be used to measure the angles for increased understanding

Learning Objective 4: By constructing this blanket, students will be able to apply the Pythagorean theorem in a hands-on way
Example: Using a ruler, the sides of any of the triangles can be measured and the Pythagorean theorem applied to them

_{Note: Inspired by the super-cool stuff at studio_Gorm}

Step 1: You'll Need. . .

1 piece of 1/2" thickness foam - 24" x 24" ¹
2 pieces of felt or other durable fabric - each 26" x 26"
Sewing machine (you could do this by hand, but a sewing machine is strongly suggested)
Ruler
Thread (either to match your fabric or contrast, depending on the look you'd like)
Straight pins
Scissors
Tailor's chalk or other marker that can be removed easily (optional but suggested)

¹You can use larger or smaller dimensions, but make sure that you're working in multiples of 6" for the foam, and that the felt is slightly larger

Step 2: All Squares Are Rectangles

Lay out one piece of felt, top with your foam, and then with the second piece of felt (making a foam sandwich)
Pin together the edges of the felt, tucking them in so the raw edges won't show
Starting at one corner measure 6" along the bottom edge, and mark with a pin
Measure another 6" inches and mark, continuing until you've reached the other corner of your felt/foam. You should have a set of parallel lines running across the felt/foam
Repeat in the opposite direction so that you have created a grid of 6" x 6" squares
Sew along the sides of the squares as well as around the edge of the felt. Try to make sure to keep all your lines as straight as possible
Remove all pins

Step 3: Trigonometric Ratios Are Key

Pin through the center of each square so that you have a grid of triangles¹
Sew along these lines, trying to keep them as straight as possible
Remove all pins, trim loose threads, and get ready to learn and play!

¹I sewed all diagonals in the same direction. For a larger blanket (or just one with slightly more structure) you would want to sew every other diagonal, and then sew through the remaining squares in the opposite direction (as shown in the image here)