Our original curved jigs were hollow underneath. This was done mainly due to the cost of the plastic that was used to make the jig. It is very expensive. Our newer ThermaJig has eliminated all of this hollow space underneath. While we have been working to make our original curved jig better, others have been trying to figure out how to copy it and produce it cheaper by making even more hollow space underneath their curved jig. Internal air volume is most critical on a curved jig. If the jig doubles or triples the internal air volume of the vacuum former, you are working against the jig, time, and your vacuum pump. It will take longer to achieve full vacuum and reduces your chance for success. Speed is critical when forming on a curved jig because you are losing valuable heat out of your kydex. Most people that have problems, get wrinkles, etc. when using the curved jig because they can achieve full vacuum fast enough and the kydex begins cooling and is no longer pliable. Our new ThermaJig may cost a little more, but the results are worth it. Less internal air volume, more curve, it is completely adjustable to the firearm and to the user. It feels solid, not cheap and flimsy, and it does not slide inside the ThermaPress VF1 and will not move while closing the lid to the vacuum former. The days of having to press down on the top of the membrane with your other hand as you close the lid are gone with the ThermaJig.