Most blended waxes you buy today are designated as either "single pour" or not. A single pour wax will usually only shrink a bit as it cools...not enough to require topping off with a second pour. Second pours can be inconvenient at best, and even a big problem if you've mis-measured and run out of wax. I hardly ever do second pours, with any wax, anymore though. I top off the candles with a heat gun. Heat guns can solve a myriad of defects and blemishes on your candles.