When it comes to varnish products, there are dozens of different ones available on the market, each with its own properties, advantages, and disadvantages.
Spar varnishes are the most common varnish products in the marine industry. Some advantages of using a spar varnish over other household-grade varnishes is the much higher level of resilience, durability, high gloss, and flexibility. Most people can recognize the natural, clear-amber color of spar varnishes that truly accentuates the grain of the wood, with an overall warm tone. These products are designed to withstand the salt spray, intense sun, and wear and tear of the marine environment. Spar varnishes will generally contain linseed or tung oil, a resin system, and a cocktail of solvents. Some have additives to boost UV absorption properties, additives to improve the self-leveling properties, faster drying properties, or additives to help reduce any air bubbles that may be created from application. Commonly, spar varnishes require sanding between coats, for best adhesion and the smoothest build. Some of the most common spar varnishes on the market currently include Epifanes High Gloss Clear Varnish, TotalBoat Lust, TotalBoat Gleam 2.0, Pettit Z-Spar Captain's Varnish, Pettit Z-Spar Flagship varnish, Interlux Schooner varnish, and Sea Hawk Captain Jack's varnish.
Similar to spar varnishes, but a different animal entirely, is the category of marine wood finishes. These products have a different composition that allows for easier application, and generally less maintenance. Many of these products will have a translucent tint to emulate a natural wood color, or a very clear look. These types of products also boast very high UV resistance, and some can be reapplied without sanding. Products in this family includes Sikkens Cetol Marine finishes, TotalBoat Marine Wood Finish, and Epifanes Wood Finish, as well as Epifanes Rapid Coat and Rapid Clear.
Two-component products comprise another group of varnishes, which require mixing a separate activator with a base component before applying. These products are much more sensitive to work with, and require the most stringent surface preparation, but they're usually the most abrasion resistant, with the highest gloss and durability among varnishes. Examples of 2-part varnishes include Interlux Perfection Plus, Epifanes PP Varnish Extra, and Bristol Finish.