Equipment required to play Paintball
Paintball is an equipment-intensive sport and in order to safely conduct a game, every player requires a marker with propellant to fire the paint, a mask to protect the eyes and face, paintballs, and a loader to hold them. To ensure safety off the playing field, a barrel sock or plug for the marker is also compulsory.
Depending on type of play, additional equipment can include gloves, a pack designed to comfortably carry pods containing extra paintballs, and a squeegee or swab for cleaning out the barrel in case a paintball breaks. Players may also elect to wear padding or armor in order to reduce the impact of incoming paintballs.
Markers.
A paintball marker is the primary piece of equipment used in 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 . 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 . Speeds above 250 are typically needed to ensure the paintball breaks on impact; the field limit is thus usually somewhere in between, often 260-280fps. The technology used to design and build paintball markers has advanced over time, beginning with the original "Nel-Spot" bolt-action pistols, progressing to pump-action markers, then to semi-automatic mechanical markers, and finally culminating in the electropneumatic paintball marker.
Propellants.
Paintball markers are powered by the expansion of gas stored in a compressed gas bottle. The two most common forms of compressed gas are carbon dioxide and high-pressure air (HPA).
Carbon dioxide.
Because CO2 becomes a liquid when compressed, it must expand to a gas in order to be used by most paintball markers, although several older models actually require liquid CO2 in order for proper operation. 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 cause damage to internal seals and O-Rings, and can "freeze" some markers, putting it out of commission for some time while it warms back up. Simple operation designs such as in-line blow-back (most Tippmanns), guns designed before HPA was more widely used, or guns using 12-gram CO2 powerlets are usually not affected by this problem, but it can still cause damage to the marker over time. 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 slightly 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.
High-pressure air or N2.
The newer high-pressure air (HPA) paintball markers use compressed air or nitrogen (N2) for propulsion, to attempt to offset issues with other types of propellants such as CO2. Due to nitrogen's low critical point, when pure nitrogen or air (which is 78% nitrogen) is compressed, it remains in gaseous form unless the temperature goes well below . When it expands, the tank also cools due to the Joule-Thomson effect, but at a far lower rate than liquid CO2 because it does not have to phase-change from liquid to gas. The lack of vaporization reduces the variation in output gas pressure associated with rapid successions of firing cycles, improving accuracy and reducing the chance of "freeze-up" malfunctions.
However, because the propellant gas is stored at higher pressures (up to ) while liquid CO2 is stored at around , HPA tanks need to be built to higher pressure ratings and are thus heavier and more expensive. The tanks themselves can either be filled with pure N2 or air (which is 78% N2). Tanks smaller than may not last heated matches, while larger tanks are cumbersome and require mounting options that create a larger marker profile.
There are two different kinds of HPA tanks in paintball. There are aluminium tanks which are preferred by younger players because while aluminium tanks are heavy and only hold about , they are also much cheaper to buy (at about USD $50, only slightly more than CO2 tanks). The second kind of tank is made from carbon fiber, which is much lighter and stronger than aluminium (being able to contain and in some rare cases , as opposed to only that an aluminium tank will hold). Generally, carbon fiber tanks are preferred by more experienced players and buyers with a larger budget, because the qualities are very reliable and have proven themselves worthy of their generally hefty price tags.
HPA tanks are generally filled from specially designed air compressors which are made to create extremely high pressures (unlike shop compressors). Although HPA tanks may, in theory, be refilled from other sources such as a conventional scuba tank or an average general-purpose air compressor, the pressure available from these sources is far below the pressure that HPA tanks are designed for. For example, shop compressors create around range, an order of magnitude less than HPA tanks are designed for (typically in the range of ). HPA tanks are filled from a nipple instead of the ASA valve, which allows them to be filled while the tank is still attached to the paintball marker.
Propane.
In 2005, Tippmann introduced the "Tippmann C3 with PEP (Propane Enhanced Performance)"; the first paintball gun to use propane as a propellent. This increased the number of balls that could be shot before needing to refill the tank (around 100 times more: which gives 50,000 shots per 470-millilitre tank), as well as having a lower gas pressure.
Comparison.
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 does not have an anti-siphon tube installed, or if there is no expansion chamber or regulator, liquid CO2 can leak into the marker, causing damage to O-rings and dangerous overpressures. The solenoid valves on electro-pneumatic markers are particularly sensitive to this, and thus many manufacturers will specify to use only nitrogen or HPA with their electro-pneumatic markers.
Nitrogen is always controlled by 2 or more pressure regulators, and generally has a more consistent shot velocity than CO2. This is because when the playing area is warm, the normally unregulated CO2 will expand more rapidly from the liquid form, causing the marker to fire at a higher velocity. When the temperature is lower, either a cool day, or from rapid firing of the marker, the expansion within the tank occurs more slowly, causing a decrease in the velocity of the subsequent shots. This is especially apparent during rapid firing while using unregulated CO2. The cooling effect of rapid discharge of CO2 causes the temperature of the liquid CO2 to drop dramatically, resulting in a significant loss in overall pressure. This effect can be greatly overcome by the use of a regulator on the tank and one on the marker, and then setting the marker up to operate well on low pressure (about 400-600 psi). Most CO2 markers are designed to operate from a bare, unregulated tank of CO2.
The proscribed act of placing a regulator at the neck of the tank will 'filter' most of any liquid escaping, but also reduce the pressure from the CO2 tank. The marker must therefore perform well under pressures significantly below the natural pressure of CO2. The second regulator is used to modulate the final pressure to a point below what the CO2 tank can deliver when relatively cold (around 500–600 psi), or warm (900–1200 psi). A qualified air smith can perform the necessary changes inside the marker to accommodate the lower operating pressure. This adds some expense to the marker but does not require access to HPA or Nitrogen refilling facilities. Some markers prefer 900–1000 psi or more, and do not work well at the lower pressures provided by CO2. This issue cannot be overcome with regulators.
Temperature has negligible effect on HPA or nitrogen, but CO2 tanks are significantly cheaper. Nitrogen tanks typically cost slightly less to fill than CO2 tanks, at approximately three to five US dollars. Also, many fields offer better rates for HPA fills due to the lower cost to the field; HPA is generally cheaper to procure as it has myriad industrial applications, and the field can even purchase the equipment to pressurize their own cylinders on-site. CO2, on the other hand, must be separated from other gases before bottling, usually through super-cooling air to the condensation point of each gas, a process that requires far more sophisticated and expensive equipment when adding regulators to prevent liquid 'splash' and to avoid a sag in pressure.
Masks.
Sometimes called "goggles", masks are safety devices that players are required to wear. These completely cover the eyes, mouth, ears and nostrils of a person. Some masks even feature throat guards. The lenses are designed to protect against paintballs traveling up to , but are not guaranteed to withstand impacts at 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, have more interchangeable parts and be made of soft enough material to get some bounces.
While playing paintball, even just shooting at the ground or trees, wearing proper paintballing masks is mandatory for safety. Some paintballs are very thick and can bounce off the ground, and other objects, and hit people.
Hoppers/loaders.
Hoppers contain the paintball supply for a marker,