Main article: Paintball marker
A paintball marker is the primary piece of equipment used in the game of paintball to tag an opposing player. An expanding gas (usually carbon dioxide or high-pressure air) forces a paintball through the barrel at a muzzle velocity of approximately 300ft/s (91m/s). This velocity is sufficient for most paintballs to break upon impact at a distance, but not so fast as to cause tissue damage beyond mild bruising. Nearly every commercial field has, and strictly enforces, a rule limiting the muzzle velocity of a paintball at or below 300ft/s* The fir* The fourth and most advanced type of semi-auto paintball marker is the electropneumatic. Here, the trigger trips an electronic microswitch (or more recently, a magnetic or optical sensor) and information is passed to a computer-controlled solenoid which releases the propellant to drive the bolt forward and fire the paintball, similar to the blow-forward design. This microcontroller operation makes the marker operate very quickly, and allows for extreme rates of fire. These markers are the most expensive (usually) of the four types and are generally used for tournament play where rates of fire can reach and exceed 30 balls per second.
There is also a strong following of stock-class and "pump" players who use markers with a purposefully low rate of fire and ammo capacity. Pump markers use a mostly self explanatory format, forcing the player to slide a pump back and forth to load each shot before fihe battlefield as your main marker can jam or run out of CO2.
Some markers are designed to look like real guns, such as the Tippmann A-5 and X7 or the Smart Parts SP8, based upon the American Prototype XM8 as well as much of the Armotech product line, and as such are called mil-sim, short for military simulation. These are used almost exclusively in woodsball and military scenario games. The more expensive mil-sim markers tend to be considerably more reliable and more rugged than most high-end speedball markers, but are heavier and tend to operate at slower, more realistic rates of fire. Most are also painted camo or black in order to blend in with foliage or shadow better than a flashy marker, since stealth and flanking tactics are of more value in the woodsball environment than that of the much smaller speedball arena. Some mil-sim markers use hoppers, though some use magazines similar to real-life automatic weapons. Many come with a shoulder stock and use a coiled remote line connected to a tank of propellant usually carried on the players back, in order to follow the mil-sim look and to lighten the marker up and make it more maneuverable.
An excellent resource on marker operation including animations of marker operation is http://www.zdspb.com/tech/misc/animations.html
i. Carbon dioxide
Because CO2 becomes a liquid when compressed, it must expand to a gas in order to be used by the paintball marker. This expansion is not adiabatic and requires energy, causing the tank to cool as heat is used to expand the liquid CO2 into gas. Eventually, under sustained fire, and especially in cold weather, the tank can become so cold that ice crystals form on it. If the CO2 bottle does not have an anti-siphon tube fitted, or is shaken while firing, the liquid CO2 may enter the marker. The liquid CO2 then passes through the marker instead of the tank, evaporating and causing the marker to freeze. This results in large clouds of CO2 vapor ejected from the marker upon firing, caused by the liquid CO2 evaporating in/around the barrel. This is known as "drawing liquid". This can and will cause damage to internal seals and O-Rings, which will put the marker out of commission for some time while it warms back up. For this particular reason, most high-end markers recommend that you use HPA. Technically, CO2 and HPA can propel the paintball, but when high rates of fire are attained, liquid is sucked into the marker which can damage or even destroy electrical components inside the marker such as the solenoid. Never leave a CO2 container in sunlight, as the heat will cause the gas to expand to a dangerous level. The tanks include safety valves in their construction, but there is no need to use them or take unnecessary risks.
With normal back-bottle setups (or, air systems utilizing a horizontal air source adapter, more commonly called an ASA), the less dense gaseous CO2 will rise to the top half of the tank. Normally, ASAs are angled with very slight angles so the gaseous CO2 is always available at the valve of the tank. Special devices known as anti-siphon tubes extend the mouth of the valve, and provide only CO2 from the top part of the tank.
During rapid successions of shots, gaseous CO2 is used up. Liquid CO2 will take some time to evaporate and rebuild the internal pressure. This process causes potentially large changes in velocity and therefore, in accuracy and range.
ii. High pressure air or N2
When nitrogen or HPA (High Pressure Air) is compressed, it remains a gas. When it expands, it also cools the tank, due to the Joule-Thomson effect, but at a far lower rate than liquid CO2 because it does not have to change from liquid to gas. The lack of this transition reduces the variation in pressure associated with rapid successions of firing cycles, improving accuracy. Therefore it is viewed as a superior source of propulsion.
However, because these propellants are stored at higher pressures (up to 5000 lbf/in² or 34 MPa) while liquid CO2 is stored at around 1200 lbf/in² (8 MPa), tanks for nitrogen and HPA are more expensive and heavier. Modern designs are usually wrapped in carbon fiber or other composite materials, to allow for thinner walls (thus, lighter weights) while withstanding the greater pressure. Average pressure for HPA tanks used in paintballing is 31 MPa (4,500 lbf/in² or 310 bar). The tanks themselves can either be filled with pure N2 or compressed air, which is 79% N2. These air sources have traditionally been used primarily by people who play often and have tournament-grade markers; however, they are becoming more popular among casual players.
Tank capacity ranges from 48 to 114 in³ (0.8 to 2 L). The 68 in³ (1.1 L) size is considered average. Smaller tanks may not last heated matches, while larger tanks are cumbersome and require mounting options that create a larger marker profile. Thus, large tanks are usually only seen in speedball back players, who do little movement but fire thousands of rounds in a game. Scenario players that fire a similar volume of paint will also utilize a large tank. 48 ci tanks are rarely seen, as a 68 is only slightly larger in form but offers a far longer play time.
HPA is also known as nitrogen, nitro, or N2. The reason for the varying name difference is because in the late 1980s and early 1990s, Tom Kaye and Team Nitro used large 114 cubic inch tanks on their back. This was the first team to use nitrogen in a paintball setting. The gas they used was 100% nitrogen, which is very rare today. The reason for this is that air compressors capable of filling tanks to the required 3000+ psi (21 MPa) are more common. HPA tanks can be filled with nitrogen or compressed air, but can NOT be filled with CO2. It is also a common misconception that paintball markers use nitrous oxide (N2O,"Nitrous", "NOS"), or NO2. Neither of these are used in paintball pneumatic systems.
HPA is also preferred because it makes it easy for frequent players to fill the air system from a conventional scuba tank. Also, many players believe that using N2 instead of HPA reduces the corrosion caused to the marker by oxidation from the oxygen in the HPA.
Nitrogen is generally preferred over carbon dioxide for a few reasons. Nitrogen will not liquefy and leak into the marker, while if the CO2 tank doesn't have an anti-siphon tube installed, liquid CO2 can leak into the marker, causing damage to O-rings. The solenoids on electronic markers are particularly sensitive to this, and thus many manufacturers will specify to use only nitrogen or HPA with their electronic markers. Nitrogen generally has a more consistent shot than CO2. This is because when the playing area is warm, the CO2 will expand more rapidly from the liquid form, causing the marker to fire at a higher velocity. But when the temperature is lower, the expansion occurs more slowly, causing a decrease in the velocity of the shot. This is especially apparent during rapid firing while using CO2. The rapid discharge of CO2 causes the temperature of the liquid CO2 to drop dramatically, resulting in a significant loss in pressure. The effect of temperature on HPA or nitrogen, on the other hand, is negligible. However, CO2 tanks are significantly cheaper than nitrogen tanks. The nitrogen tanks traditionally cost slightly less to be filled than the CO2 tanks at approximately three to five US dollars. Also, many fields offer better rates for HPA fills due to their lower shots per fill (more apparent in smaller HPA systems, such as a 3000psi, 48ci tank) than CO2; the most common being 25 cents per ounce for CO2 and $5 for all-day HPA fills. From this, it can be seen that for the cost of refilling a single 20 oz. CO2 tank, a player can refill any size HPA tank all day.
Sometimes called "goggles", masks are safety devices that players are required to wear. These completely cover not only the eyes, but also the mouth, ears and nostrils of a person. Some masks even feature throat guards. The lenses are designed to stop paintballs traveling around or under 300ft/s (~90m/s). It should be noted, however, that the lenses are not designed to withstand impacts of paintballs traveling at vastly greater speeds.
Double-layered or "thermal" lenses are also available. These lenses are much less prone to fogging. These work by separating an inside and an outside lens with an air chamber, that allows for the difference in temperature between the inside and the outside of the mask without forming condensation. However, if any moisture whatsoever somehow gets in between the two lenses, the inner faces of both lenses will fog, and it will take a very long time to dry out, if it does at all.
Fogging masks can be a significant hazard while playing. Besides the lost vision, players may be tempted to remove their mask and expose themselves to serious eye injuries. To reduce fogging of lenses while playing, some masks include electric fans that remove humidity and dry the lens. This is especially useful for situations that require wearing the mask for extended periods of time, such as wood play, large games, or being a referee. Finally, there are many anti-fog topical solutions that players can apply .
The exterior of the thermal lenses (or the lenses, in non-thermal masks) is usually made of Polycarbonate. This material provides excellent impact resistance. Because polycarbonate is soft, these lenses are manufactured with anti-scratch coatings. But great care must be taken to keep proper care of the lenses. Many vendors recommend the immediate replacement of very scratched lenses, or lenses subjected to very strong impacts.
Generally, more expensive masks tend to be smaller (which in turn makes the player a smaller target), more comfortable, and have more interchangeable parts.
It should be noted, that while playing paintball, even just shooting at the ground or trees, wearing proper paintballing masks are mandatory for safety. Some paintballs can be very thick and can bounce off the ground, and other objects, and hit people.
Main article: Paintball marker#Hopper
Hoppers are the means by which a paintball player keeps their marker fed with ammunition, much as magazines are to a regular rifle. With few exceptions, hoppers are all mounted above the marker, and most use gravity as the ultimate force to get the balls in the marker. That is to say, if most hoppers are turned upside down, the marker will not be fed with balls. There are two main types: Gravity feed, and Agitated Feeders. Gravity Feed hoppers often get jammed up with balls at the feed neck, which can result in a marker 'dry firing' (firing without paint) or chopping balls due to the timing of the ball entering the marker. This is detrimental to the performance of the marker and speed of shooting. Agitated Feeders, sometimes generically known as revies, improve on this method of feeding the marker. Though a few actually force the balls down the tube when needed, most simply use some method, from agitation to revolution of a wheel inside the hopper, to shake up the balls and send them down the tube. Using various methods, hoppers have been able to achieve rates of feed 30 balls per second and above(Vlocity). A special type of hopper, called a helixal fed hopper, feeds balls using a spring driven helix shaped tube. These special hoppers can be mounted under a barrel, giving the marker a much lower profile. In addition to a lower profile, they can also achieve the highest feed rates in a paintball hopper- about 30 BPS (balls per second). The most commonly seen is the Q Loader. There is some confusion about the term 'loaders.' Though a loader can often refer to a Agitated hopper, the term is also used for gravity hoppers, and some people use the word to refer to guppies/pods used simply to carry extra paintballs.
Paintballs, also simply called "paint", are spherical gelatin capsules containing primarily polyethylene glycol, other non-toxic and water-soluble substances, and dye. Paint is made of materials found in food and are edible, but taste bad.  Early paintballs were made of glass  and filled with indelible oil-based paint, since they were made for marking trees and cattle, but modern paintballs should easily wash out of most clothing. The color of the shell does not necessarily indicate the color of the fill.
Most common paintballs and paintball markers are described as .68 caliber, but many factors affect the exact dimensions. Paintballs and barrels vary in size from .67 caliber to .71 caliber. On most paintball markers, the barrel must be slightly larger diameter than the paintball for correct operation. In addition, paintballs are seldom perfectly round and are very sensitive to heat and moisture. A hot or humid day may result in paint swelling or becoming misshapen. Care should be taken to keep paintballs out of the sun and away from moisture. An insulated cooler works well for this on the field.
Generally speaking, paintballs of greater price are subjected to more stringent manufacturing processes, quality checks, and standards, making their size and shape more consistent. This is very important for accuracy. Better paintballs also tend to have higher quality fills and thinner shells to improve the frequency of breaking on impact rather than bouncing, and thus raise the percentage of "eliminations."
SWAT teams often use paintballs filled with a pepper substance (known as a pepper ball) as a non-lethal incapacitation method.
Paintball is a very active sport, involving a lot of running, diving, crawling and sliding. Accordingly, the clothing worn for paintball must be extremely hard-wearing and durable. For woodsball, camouflage is also extremely useful, so it is not uncommon to see players wearing army surplus military fatigues or BDU (Battle Dress Uniform), particularly DPM styles. For speedball, however, the small field and artificial obstacles make camouflage ineffective. Speedball players therefore wear clothing which forms a uniform amongst the players, usually in threatening colors or styles (flames, for instance, are particularly popular). For scenario games, players will tend to dress themselves in a style appropriate to the character or force they are representing.
Clothing worn for tournament paintballing is also constrained by the tournament rules, which expressly prohibit thick padded materials which are likely to adversely affect the chance of paint breaking on the target. Combined with the need to allow adequate padding to protect the elbows and knees during slides on hard ground, tournament paintball gear can take on a rather unusual appearance. Often, in an attempt at gamesmanship, players will wear the baggiest clothing they can reasonably get away with, as this also makes paint more likely to 'bounce'.
Footwear varies enormously between Speedball and Woodsball/scenario games. In woodsball, the rough terrain and uneven, often muddy ground makes footwear with good grip and plenty of ankle support a necessity. This lends itself to boots, either military style or walking/hiking boots. In speedball, however, the added weight of thick boots is a distinct disadvantage, as is the reduction in mobility. Speedball players therefore tend to wear sneakers or cleats.