I have an 8.5x11.5 area rug over berber. I tried an inexpensive mat thinking maybe I could get the job done with $35. The mat turned out to be a complete waste--the rug continued to wrinkle and I was often needing to move the couch, roll up the rug, unroll, smooth it out, repeat...DON'T WASTE YOUR TIME!
I found Ulitmat by Jade Industries online. It was more costly, but I needed something that would WORK. When it arrived I laid the "rough" side on the berber and put the rug on the rubbery side. I marked the shape of the rug, offset by about 1", on the rubber side of the mat. This is important b/c the rug may not be perfectly rectangular. I cut along the markings and put the mat and rug into position. With the scraps I cut pieces to go under the feet of my sectional, rough side on the rug & rubber side contacting the feet. Now my rug stays flat AND the couch stays in place! BONUS!
TIP: buy Ultimat oversized and cut it to w/in 1" of the edge of your rug to avoid a "step-effect."

this worked out very well. Delivered quickly and easy to cut and install.
Great!

I tried everything to try to get my rug to not slip on very small-loop berber carpet that is slippery; various rug pads from other stores, double-sided tape, etc., didn't work. I decided to buy this based on another reviewer's similar experience, and yay! It works! It's been 4 days now and no moving or tugging or bunching! I really didn't think anything would work. Thanks.

With so many mats available out there its easy to try to save on the mat, especially when buying a rug that already costs a pretty penny! But I'm so happy I decided to go for this mat as I keeps my beautiful rug perfectly flat and fixed on the bare floor. I am so pleased that I ordered the same product in an even larger size for my living room rug. I believe it will help keep my rugs looking great for many more years!!