You can use more sheets of WSS and not rinse it out. Just cut away the extra.

I use two layers of wash away and run just enough HOT water over the item to melt most of the wash away off and it's still pretty stiff. I do a lot of FSL....Badge Master is good too.

i use 2 layers of wash away and then i just disolve the it in warm tap water and hang in the sun or a warm place i did some angles and they are stiff.
Marlene

I have stitched the design twice and glued them together. It was for a mobile and I wanted both sides to be the same since they would be twirling around. It was a lot of work and I made a bunch of the moblies so as long as you aren't doing too many is shouldn't be a big project.I don't wash me FSL a lot either and that keeps them stiff and a little thicker. I also use Badge Master,2 layers and have very little trouble.

I'm not quite sure what you mean by "heavy" but if you don't mean stiff (which is what the other suggestions would do) but instead mean thicker, you could use two threads on the top (just run them side-by-side together and thread them through the same needle, although you will need a needle with a large eye) or you can try to find a heavier thread (a 30 wt rather than the typical 40 wt). Cotton thread tends to look heavier than polyester, and rayon usually looks lighter. However, if you use cotton, be forewarned that it will leave behind a LOT more lint, so be sure to clean out your bobbin case and thread run thoroughly when you are done.

Try using overlocker thread.

thanks ladies I just thought how to do it from all your ideas
I will make 2 Dolphines and sew together but put something inside
I am makeing table weights to hold a table cloth down out side on each corner

How about leaving a little opening and putting son bb's inside? the ones for bb guns?those little pellets are heavy!!!