As you wrap the felt strips, keep one side of the trivet flat, but don't worry if the reverse is uneven (that side can face the table). These instructions can also be used to make coasters.
Martha Stewart Living
Cut felt strips, about 16 inches long and 1/2 inch or 1 inch wide, from 3 colors of felt (cut 14 strips in tan, 12 in medium brown, and 5 in dark brown for a trivet that's 5 1/2 inches across).
Starting with a tan strip, apply a dab of fabric glue 3/4 inch from 1 end. Begin rolling felt strip tightly over the glued area, pressing to secure. Continue rolling, applying glue as you work, until the coil measures no more than 1/2 inch across. (If the coiled center grows too large, the trivet will begin to resemble a bull's-eye rather than a stump.) Snip off end of felt strip.
Apply fabric glue to 1 end of a medium-brown strip. Position end at the snipped end of the tan coil, pressing to secure. Wrap medium-brown strip 1 or 2 times around tan coil, applying glue as you work. Snip off end of felt strip.
Continue to wrap felt strips around coil, alternating colors, 2 to 4 times for each tan strip and 1 or 2 times for each medium-brown strip, until stump reaches 5 to 7 inches in diameter (3 inches for coasters); end with a medium-brown strip.
Wrap 2 or 3 dark-brown strips around trivet or coaster, gluing as you work. To create a textured-bark effect, cut dark-brown felt strips into 1/2- to 2 1/2-inch-long strips; layer on outer edge of trivet or coaster, gluing as you work.