The clumping of brown sugar is the result of the molasses coating drying... There are terracotta pieces sold to reduce or prevent the drying effect.  They are soaked in water, wiped dry and placed in the container to help retain moisture.. Being a cheap sort and

one that would rather make rather than buy , I ended up making my own terracotta moisture maintainer..I purchased a new flower pot, soaked in water for a couple of hours then cut it into pieces starting with the rim. To do this I used a thin masonry disc on my

4 1/2" angle grinder. It worked amazingly well, with the only drawback being dust. All corners and edges  of the pieces were rounded too finish things off. Some of the pieces are small enough to fit in my smaller shaker jars .. All this for $2.00 and some time.

I've had some luck popping the brown sugar in the microwave for a few seconds at a time, then kneading it until it's uniformly moistened. Have you tried that?

I keep it in the fridge.  Always soft, never clumps.

I used brownulated sugar that doesn't clump.

Little cloth reusable tea bags with rice in them, here.

I've had some luck popping the brown sugar in the microwave for a few seconds at a time, then kneading it until it's uniformly moistened. Have you tried that?

No. However my main issue is with rubs containing brown sugar..I wouldn't want to nuke them. Thanks for the tip.

I used brownulated sugar that doesn't clump.

Ditto. in addition, granulated brown sugar mixes well in rubs and sprinkles without clogging the shaker.

 
 I checked out " brownulated " sugar only to find out, it's available only in US..Too bad.

 I checked out " brownulated " sugar only to find out, it's available only in US..Too bad.

I have used Turbinado sugar at times as a replacement but in smaller quantity.

I actually dried brown sugar by putting it on a cookie sheet and spreading it out. Set the oven for 250 for ten minutes, but kept checking it. Worked like a charm. Pretty happy and my 1lb of rub is clump free also.

My wife just bought a set of 4 clay pieces to keep her brown sugar from clumping

You can also take a citrus peel and place in the bag to bring the softness back.  I learned that trick back when I used to deal with a...ahem, certain herb...

If you reseal the package tightly without any air, it will extend the its usability. I lightly vacuum pack mine after each use, clumping has not been a problem since I started this method.

I have a container for storing coffee that I got from the container store that worked pretty good at first.
It has a rubber seal around hockey puck for lack of a better term.
You push it down and all the air gets forced out.
Then put the lid on which has a silicone gasket around it.
Doesn't work so well anymore.
Need to come up with a plan B.
That Brownulated sugar sounds interesting.

That Brownulated sugar sounds interesting.

It was great but I think Domino quit selling it in small boxes and bags.  I just thru about 10 bags out a month or so ago as they were about 7-10 years old.