Survival knives are knives which have been designed to be used in wilderness or survival situations. They come in a variety of designs and are one of the most valuable additions to your pack. However, because you will find being sold many varieties of knives described as survival knives it is important that you pick a good quality, robust knife with the correct construction and features.
One of the most important features of good quality survival knives is one that is not be apparent to the eye but is vital to the strength of the knife, and that is that it be constructed with what is known as a full tang. The tang of the knife is the extension of the blade metal into the handle. In some cheaper knives, the blade can be screwed and glued to the handle, whereas with a full tang part of the handle is the blade, which of course eliminates this weak spot. If a knife cannot be relied upon to cope with hard regular use, then it cannot really be called a survival knife.
There are two materials which are used in the construction of survival knives, stainless steel and carbon steel. Stainless steel blades are the most common and have the advantage of being rust-resistant, an important quality in a damp environment.Carbon steel blades are not rust-proof and will need to be regularly oiled to keep them in good condition, however, considering that they can be sharpened to a keener edge and will hold that edge longer than a stainless steel blade; it's really depends one one's needs.
Survival knives have two edge types - serrated and smooth-edged. Serrated blades are better at cutting through meat and light sawing whereas a smooth-edged blade is better at carving, skinning and food preparation. I personally find a smooth edged blade to be more versatile, as they are far easier to keep sharp using locally sourced materials. A serrated blade needs a specialized tool which could be easily lost in a survival situation or not even brought in the first place! Some serrated knives have a saw-toothed top of the blade for wood cutting although I find their short length tends to limit their effectiveness. Also, it makes it difficult to apply pressure to the back of the knife, for example when splitting wood.