What is the difference between Pillar Waxes and Container Waxes,

 Pillar Waxes are in general harder and are designed to shrink during the cooling process, this allows your candle to  to release from the mould,  Pillar Waxes are designed to be out of a container and free standing, whereas Container waxes are softer and need to be placed into a container and remain there.. If you try and use a container wax in a pillar mould then you will not be able to release the wax from the mould, on the other hand to use a Pillar Wax in a container will lead to the wax shrinking from the sides and in some circumstances the wax will fall out of the container.

However when making soy melts /tarts as they are going to be just melted in a oil burner the fact the pillar wil shrink back from your original mould is no longe relevant. In fact some people prefer to use Pillar as it is easier to demould from your small moulds.

As Kevin rightly said however , if you are making a very intricate melt using a intricate mould because the pillar is harder and therefore more brittle you are at greater risk of damaging your final product. The solution to this with a intricate mould is to combine the types of wax or use container only