Sew Basics: Dealing With Heavy Material
If you are having trouble getting a needle to penetrate thorough a particularly heavy material, rub a little beeswax (or candle wax) along the thread. The wax works as a lubricant, and the whole stitching process will be less stressful on the fingers and wrists.
You can also use beeswax to stop the end of a reel of cotton from unravelling, or to hold thread onto a spool as you fill it. A tiny blob of wax is sticky enough to keep a cotton thread in place, but weak enough to pull away if the cotton is placed under tension.