According to Shooting Illustrated
In the past, we’ve discussed the importance of selecting a defensive holster that is specifically made for the model of pistol that a person carries. And, we’ve also talked about the importance of having a defensive holster of the best quality possible so that it holds the handgun securely. Both of these are important considerations whether that holster is made from cowhide, horsehide or Kydex.
Another important consideration is selecting a belt that will hold the handgun and holster securely in one spot. The belt should be made of thick material so that it doesn’t sag under the weight of the gun and holster. And, it should be the same width as the belt loop on the holster so that it doesn’t allow the holster to slip around. It is rare that one can find belts like this in the big-box store at the local plaza. That’s the reason that I buy my belts from holster makers, because they understand the important role the belt plays in concealing and securing a defensive handgun.
Something not often discussed when talking about defensive holsters is that the shooter should be able to get a shooting grip on the pistol the instant the hand comes in contact with it. Most current-production holsters have a space between the front strap of the pistol and the top of the holster, but they often do this because it is the current style and don’t really understand what it is designed to accomplish.