If you cast resin and you can only buy one tool right now, buy a pressure pot. For clear, solid castings - dice, paperweights, jewelry, river tables, tumblers - a pressure pot is the reliable answer because it shrinks trapped bubbles until they are invisible at 30-60 PSI, instead of trying to pull them out the way a vacuum does. A vacuum chamber earns its place when your main job is degassing silicone mold rubber before you pour, or when you cast porous materials like wood, plaster or foam where pressure cannot reach the trapped air. The short version: vacuum removes air before the pour; pressure shrinks whatever air remains during the cure. The five real options compared in the table below split cleanly into those two camps, and your project type decides which one you actually need.
The bubble problem, and the one decision beginners get wrong
Every resin caster fights bubbles. They come from air whipped in during mixing, air released by the chemical reaction as the resin kicks, and air trapped in the surface of a mold or an embedded object. The mistake beginners make is buying the wrong machine for the wrong stage of the problem. They watch a video of someone degassing silicone in a vacuum chamber, assume that is how you clear a clear resin casting, buy a vacuum kit, and then get a glass of foaming “beer” instead of a glass-clear paperweight. The two tools solve the bubble problem at different moments and by opposite physics, and once you understand that, the choice gets easy.
How a pressure pot works: 30-60 PSI shrinks bubbles to invisible
A pressure pot is a sealed steel tank. You pour your resin, place the piece inside, clamp the lid, and feed compressed air in until the gauge reads your target - most makers run 30-60 PSI for clear resin. The pressure does not remove the bubbles; it crushes them. Under pressure, every trapped bubble shrinks toward the point where it is too small to see, and the resin cures with the bubble locked in that tiny state. The single rule that makes or breaks the result: you have to hold the pressure until the resin reaches its gel point, which for a medium-working-time epoxy is most of its 20-40 minute working window. Release pressure too early and the bubbles expand right back as the gas inside them decompresses. Smooth-On’s casting guidance points to around 60 PSI for the clearest demanding casts, and a pot like the California Air Tools 365C is rated to 80 PSI tank pressure for exactly that headroom.
Pressure is the right tool for solid castings where the air is already mixed into the resin: dice, coasters, jewelry blanks, tumblers, deep-pour river table sections. If you want a deeper walk-through of the actual workflow, see our how to use a pressure pot for resin casting guide.
How a vacuum chamber works: ~29 inHg pulls air out before the pour
A vacuum chamber does the opposite. It is a sealed chamber - usually with a clear acrylic lid so you can watch - connected to a vacuum pump that sucks the air out. Pulling down to roughly 29-29.6 inHg (about 75 cmHg) of negative pressure makes any dissolved or trapped air expand, rise, and pop at the surface. A full degas cycle takes a couple of minutes: the mixture foams up dramatically, peaks, and then the foam collapses as the air leaves. That is exactly what you want for silicone mold rubber, which is thick, holds air stubbornly, and has a long enough pot life to survive the foaming. Vacuum is also how you pull air out of porous embeds - dried flowers, wood, plaster - before they bleed bubbles into a casting.
Where vacuum struggles is thick-mixing clear casting resin. The same foaming that degasses silicone can become a runaway “beer-foam” effect, and a fast-kicking resin can start to thicken before the foam fully settles, leaving bubbles stranded. That is the core reason the comparison table below routes clear solid casts to pressure, not vacuum.
The comparison table: pressure and vacuum, side by side
The comparison table below lines up all five options against the numbers that actually matter - type, capacity, the pressure or vacuum each one delivers, pump CFM, and what each is genuinely best at. Read it as two families: the two pressure pots (TCP Global 2.5 gal and California Air Tools 365C 5 gal) for clear solid casting, and the three vacuum options (Zeny 3 gal kit, VEVOR 3 gal stainless kit, and the bare VEVOR 2 gal acrylic chamber) for degassing. The price bands tell the same story your project should: a pressure pot kit starts cheaper than a full vacuum kit if you already own a compressor, while a vacuum kit is cheaper as an all-in-one because the pump is in the box.
Decision by project type
This is the fastest way to choose. Match the work to the tool:
- Dice, jewelry, coasters, paperweights, tumblers, pen blanks, solid clear casts - pressure pot. These are solid resin pieces where bubbles must become invisible. Pressure wins every time.
- River tables and deep-pour blanks - pressure pot, sized up. A 2.5 gal pot is too small; the California Air Tools 5 gal fits taller and multiple molds.
- Silicone mold making (pouring rubber over a master) - vacuum chamber. Degassing the silicone before it sets gives you a bubble-free mold, which then gives you bubble-free castings forever after.
- Porous embeds - wood, plaster, dried botanicals, foam - vacuum chamber to pull trapped air out of the material before casting; pressure cannot reach air locked inside a porous solid.
- You do a bit of everything - you will end up owning both, but start with whichever describes your most common job.
Decision by budget
If you already own an air compressor, the pressure path is the cheapest entry to glass-clear results: the TCP Global 2.5 gal kit runs $65-$90 and you are done. If you do not own a compressor, factor that in - a small quiet pancake compressor is plenty since the pot only needs topping up to hold pressure, not constant airflow.
On the vacuum side, the math flips. A complete kit like the Zeny 3 gal ($85-$120) or VEVOR 3 gal stainless ($90-$140) includes the pump, hose and oil, so there is nothing else to buy. The bare VEVOR 2 gal acrylic chamber ($40-$70) is only the cheapest option if you already own a vacuum pump - budget another $60-$90 for one if you do not. Our best vacuum chamber for resin roundup goes deeper on chamber-plus-pump pairings.
When you actually need both
Professionals own both because the cleanest possible workflow uses each at its right stage: vacuum the silicone mold to degas it, then pressure-cast the resin into that mold. Air out of the mold, plus crushed bubbles in the resin, equals near-perfect clarity. The California Air Tools 365C is built for people heading this direction - it accepts the 365VK vacuum kit so a single tank can pull vacuum and then hold pressure. For most hobbyists, though, that is a phase-two purchase. Buy the tool your current work needs, get good with it, and add the second machine when a real project demands it.
The spec table explained: PSI vs inHg/cmHg, CFM, capacity
The units in the specs below trip people up, so here is the plain reading. PSI (pounds per square inch) is positive pressure - it is what a pressure pot pushes into the tank, and bigger is more crushing force on bubbles; 30-60 PSI is the working range, 80 PSI is the tank rating ceiling on the 365C. inHg (inches of mercury) and cmHg (centimeters of mercury) measure negative pressure, or how hard a vacuum pulls; about 29-29.6 inHg is “near full vacuum” at sea level and is what you need to degas silicone. Pa (pascals, shown as ~5 Pa) is the ultimate vacuum a pump can reach - lower is stronger - and is mostly a spec-sheet bragging number for hobby work. CFM (cubic feet per minute) is how fast the pump moves air; 3.5 CFM single-stage is comfortably enough for hobby degassing. Note that capacity numbers describe the chamber or tank volume, not how much resin you mix.
Pressure pot picks: TCP Global 2.5 gal vs California Air Tools 365C 5 gal
The TCP Global 2.5 gal is the standard beginner buy and for good reason: it is a steel tank with a clamp lid, regulator and a 0-100 PSI gauge, it holds the 30-60 PSI window resin needs, and the ~9.35 in diameter by 10.25 in deep interior swallows dice molds, jewelry trays and coaster molds easily. The honest caveat is that it ships as a paint pressure pot - you should remove the factory dip tube and fluid feed parts before using it for casting, which is a five-minute job. Our best pressure pot for resin guide covers that conversion in detail.
The California Air Tools 365C 5 gal is the upgrade: purpose-built for resin, Teflon-lined so cured drips peel off, rated to 60 PSI operating and 80 PSI tank, with casters and a 5 gal interior that fits tall or multiple molds. It costs three to four times the TCP Global, so it only makes sense if you cast volume, do deep pours, or want the 365VK vacuum option down the road. For small jewelry-and-dice work, it is overkill.
Vacuum picks: Zeny vs VEVOR 3 gal kits and the budget 2 gal acrylic chamber
The Zeny 3 gal kit and VEVOR 3 gal stainless kit are near twins on paper - both 3 gal chambers with a 3.5 CFM single-stage 1/4 HP pump pulling to about 29 inHg, both complete with hose and oil. The practical difference is the body: VEVOR’s stainless steel chamber resists corrosion and dents better than thinner steel, while Zeny pairs a steel base with a clear acrylic lid you can watch the degas through. Both single-stage pumps are right for hobby degassing and top out below what a two-stage pro pump reaches for fine lab work.
The VEVOR 2 gal acrylic chamber is the odd one out: it is chamber only, no pump. Its thick ~18 mm acrylic walls hold a strong vacuum (it holds vacuum for around 24 hours with about 5% leak over 12 hours in reported testing), and being fully transparent you see the whole batch, not just the top. It is the cheapest path to degassing only if you already own a pump - otherwise the separate pump erases the savings.
Safety: PSI ratings, relief valves, and acrylic lids
Two safety rules are non-negotiable. First, a pressure pot must be rated for the PSI you run it at, and the relief valve must work - never improvise a casting pot from a random paint pot without verifying the pressure rating and testing that the relief valve actually vents. A steel tank failing at 60 PSI is dangerous. Second, acrylic vacuum lids and chambers are wear parts. Acrylic can craze, cloud and eventually fail under repeated vacuum cycles, so inspect the lid for cracks before every session and replace it at the first sign of crazing.
On chemicals: mixing and casting resin releases fumes, and degassing or pressurizing does not change your ventilation needs. Work in a ventilated space and use a properly rated organic-vapor respirator for extended sessions - our resin safety and respirators guide covers what cartridge to use. Never seal a corrosive chemical in an oil-lubricated vacuum pump kit; these kits are rated for resin, silicone and gypsum, not aggressive solvents.
Troubleshooting the two methods
Beer-foam in the vacuum chamber. If clear resin foams up and threatens to overflow, you mixed a resin that is too thick or too fast for vacuum. Use a taller container with lots of headroom, “bump” the vacuum (release and re-pull) to knock the foam down, or simply switch to a pressure pot for that resin. See epoxy resin bubbles - how to fix for the full bubble playbook.
Bubbles re-expand after releasing pressure. You released too early. Hold pressure until the resin has gelled - for most medium-cure epoxies that is most of the 20-40 minute working time. As a rule of thumb, the resin should be past its tacky working stage before you crack the lid. Typical epoxy hits ~95% cure in 24 hours and full cure in 72 hours, but you only need gel for the bubbles to stay locked.
Pour depth matters too. Arts-and-craft (table-top) resin pours roughly 1/8 in per layer; deep-pour resin handles 2-4 in per pour with re-pour layers every 8-10 hours. Over-pouring a table-top resin traps heat and bubbles that no machine fully fixes - match the resin to the depth first.
Verdict
Buy a pressure pot first if you cast resin. The TCP Global 2.5 gal at 30-60 PSI delivers glass-clear dice, jewelry, coasters and tumblers for $65-$90 plus a compressor, and it solves the bubble problem the way solid castings actually need - by crushing air during the cure. Add a vacuum chamber when degassing silicone molds or casting porous materials becomes your main job. The serious-maker endgame is owning both and using vacuum on the mold then pressure on the resin, but as a single first purchase for resin work, pressure wins.