The most important piece of tack you can invest in is your saddle. The second most important is your saddle pad (or half pad for English riders). Multiple studies have consistently ranked wool as the best material you can put on your horse's back. It is thermoregulating, moisture wicking, breathable, and durable. The holes from the canvas the wool is latched onto provides further breathability. Gel traps heat and is heavy. As a former saddle fitter, it was never a material I would recommend to my customers. Foam comes in many types and varies greatly. The two main types of foam will be open cell and closed cell. Open cell is form fitting (think a memory foam mattress ) and typically used to fill in gaps caused by poor saddle fit. This type of foam can "bottom out" under too much weight and does not offer much by way of shock absorbtion. Closed cell foam provides somewhat better shock absorbtion but traps heat more. In general, foam will trap heat more than wool but less than gel. It is heavier than wool but typically lighter than gel.
Not all wool pads are created equal, though. Many mass produced "felt" pads are not pure wool and are a blend of wool and synthetic. One big benefit of pulled wool is that it will felt down with use and give your horse pressure point relief where needed, similar to open cell foam but with out the bulk or heat trapping.
A similar concept applies to your cinch. Leather cinches require conditioning and can get moldy in damp environments. Neoprene, foam or gel lined cinches, and synthetic fleece trap heat. Synthetic cord cinches will stretch out over time. Be wary of cinches labeled "mohair blend" or "wool blend". There is no way of knowing how much of the cord is mohair vs wool or synthetic and these cinches will usually stretch out or shrink up. While wool is a great material for saddle pads, it's not recommend for cinches as it will felt and the length of your cinch will change over time. This is where mohair shines. Nicknamed the "diamond fiber", mohair is incredibly strong, durable and will not stretch out or shrink up. Mohair cinches are breathable and will gently expand with your horse's ribcage. They are great for horses prone to galls or horses with sensitive skin. Mohair cinches will be lighter weight than most mass produced cinches as well, making them an excellent choice for endurance riders. Alpaca is extremely similar to mohair with the main differences being that it is softer, felts more easily, and comes only in natural colors while mohair can be dyed. Both are great options for cinches.
When it comes to take longevity, durability, and comfort of your tack, natural materials can't be beat.
