It is super easy. I made one today for my mom for Mother's Day!
I had recently bought a roll of adhesive magnetic material for another purpose that did not work out so well and decided to try to make something else. What came to mind was refrigerator magnets and magnetic Bumper Stickers.
First off, grab yourself some magnetic material at Amazon (affiliate link) Magnetic Sheet Roll for Crafts, Signs, Display - Flexible 24" X 30" Magnet
Because of the type I bought, one side being adhesive, I used a sheet of cardstock, cut to size, for moms refrigerator magnet. Also, I made it rather large due to her poor eyesight.
This particular magnet is not waterproof, however you can use the non adhesive magnetic roll and vinyl. I chose not to use vinyl because having two adhesive sides together...well, for me...no good could come of that! LOL
I purchased the design from the Silhouette site and cut it out of adhesive cardstock to place on top of regular cardstock. The design was actually for a card and I just used this half of the card. Next I added washi tape around the edges to fancy it up some. Last but not least, I used three small embellishments in the center of the flowers; pink, yellow and white.
This is such an easy project that only took about an hour once I had my supplies gathered!
It is certain to be just as easy to make your own magnetic bumper stickers, and they will be personalized to your own taste and preferences! I would use Oracle 651 for a bumper sticker so it would be sure to last through weather changes. Needless to say, I am off to make a bumper sticker right this very minute!