With its patent-pending design, Thundershirts gentle, constant pressure has a dramatic calming effect for most dogs, if they are anxious, fearful or over-excited. Pressure has a calming effect on the nervous system and is used to reliever anxiety. Thundershirt is an excellent treatment for most types of dog anxiety and fear issues. For many anxieties, we recommend just putting on a Thundershirt and observing the results (No training!). You very well may see significant improvement for noise, crate, travel, barking and others with absolutely no training. For more complicated anxiety cases, we recommend using Thundershirt as part of a behavior modification program. On thing is for certain, for a very large percentage of dogs, Thundershirt"s gentle, constant pressure has a terrific calming effect. This has obvious benefits for most types of anxiety. But Thundershirt is also a very useful tool for managing excitability or hyperactivity with strangers, on the leash, or in a training environment. Thundershirt"s calming effect helps a dog to focus (or refocus) her energies in a more constructive direction, allowing training to be more effective. Grey only. Measurements: X Small - chest: 13"-16" (10-18 lbs).