What are they made of? Sandpaper?

No. They are strips of flexible acrylic (my best guess) about 1/8" thick with adhesive on one side (the side that attaches to your existing ruler). The website tries to show how having these on the outside edges results in equalized pressure to the edges of your ruler.

I have some grip strips and yes they work well but, I found that you can use the Nexcare brown rubberized waterproof tape on a roll on rulers. It is removable without leaving any residue and is reusable.

I've been using these for several months and have re-ordered enough to put on all my rulers! They really work great. Their online service is good too, and orders take less than a week to reach you.

I absolutely LOVE them!! I just ordered 2 sets... I had some that didn't quite stick onto one of my rulers. I emailed the company and they sent me 2 replacement strips.

I will *definitely* order more in the future!

They made me a more confident cutter! Wouldn't be without them.

I bought some - but dont 'save' them.. use them as the glue gets funky. mine were prob 6 months old.
I wasnt impressed .. they did hold in place but they made the ruler a bit too high off the fabric if you get my meaning..

creative grids is still my number one choice..

I like Bonnie Hunter's solution to slipping rulers - use 3M NexCare flexible clear tape found at the drug store or WalMart really cheap. One roll will be sufficient for many rulers &/or templates.

I use OLFA frosted rulers....have no problems with slipping:D

I received my two packs rather quickly, have to say that they do wonders for slippery rulers. Glad I found out about them, could have used them years ago.