The pictures above are vintage patterns. The most popular pattern is the two toned cozy where the knitting pattern pulls the yarn tightly behind as it is knitted, giving the cozy extra thickness which would allow for great warmth. The best yarns or fabrics to make a tea cozy are cotton and wool. Cotton and wool help the teapot maintain the warmth and keep the teapot warm longer than a bare teapot exposed to the elements. Cotton is usually easier to wash and less expensive than wool, so it is a favorite to make cozies out of. Acrylic yarn is also much easier to wash and it is less expensive than wool, so it is also a favorite among knitters.
Is it a Tea Cozy or Tea Cozie? Both are fine, but the Cozy is most popular and used more in the countries where tea cozies are used most often.
In order for a tea cozy to fit correctly and do the job, it needs to be tall enough to touch the table all of the way around and fit over the pot. If it has openings for the spout and handle, measure the teapot from the table to the beginning of the spout and from the table to the beginning of the handle. Then measure the end of the spout and handle. Are the openings large enough to accommodate the handle and the spout you wish to use the cozy on? Some handles are taller than the spouts and vice versa. Due to this knowledge, some cozies have openings from the bottom to the top or may have one side opening larger than the other side. If the tea cozy fits correctly, it must be tall enough to touch the table and not allow cold air to go under it.