CPAP vs APAP vs BiPAP: Which Machine Is Right for You?
Last updated August 2026
CPAP, APAP, and BiPAP are all positive airway pressure (PAP) machines that keep your airway open during sleep, and they differ mainly in how they deliver pressure. CPAP blows one fixed pressure all night. APAP automatically raises and lowers pressure moment to moment as your airway needs change. BiPAP uses two separate pressures, higher when you inhale and lower when you exhale, for people who need high pressure or have trouble breathing out against it. Most new obstructive sleep apnea patients do well on CPAP or APAP; BiPAP is reserved for specific medical situations.
Medical note: PAP therapy is a prescription treatment. The machine type, pressure settings, and mask are decided by your sleep physician based on your sleep study, and self-adjusting settings or buying a machine without a prescription can be unsafe. Use this article to understand your options and ask better questions, not to diagnose or treat yourself.
What all three machines have in common
Sleep apnea, in its most common form, is a mechanical problem: the soft tissues at the back of your throat relax and collapse during sleep, blocking airflow. Every PAP machine solves this the same way, by using a small blower to deliver a gentle, continuous stream of pressurized room air through a tube and mask. That air acts like a pneumatic splint, holding the airway open so you stop snoring, stop having breathing pauses, and stop the repeated micro-arousals that wreck your sleep quality. The differences between CPAP, APAP, and BiPAP are entirely about how the pressure is managed, not about whether they treat apnea.
If you want the full picture on diagnosis, masks, humidification, and getting comfortable, our CPAP buying guide covers the therapy end to end, and the CPAP and BiPAP machines hub rounds up current devices.
CPAP: one fixed pressure, all night
CPAP (Continuous Positive Airway Pressure) is the original and still the most widely prescribed therapy. Your doctor sets a single pressure, measured in centimeters of water (cm H2O) and usually somewhere between 4 and 20, and the machine holds that pressure whether you are inhaling, exhaling, lying on your back, or dreaming.
Best for: People whose apnea is well controlled at a steady pressure, and anyone who wants the simplest, most affordable, most reliable option. Because there is less to go wrong, CPAP units tend to be the least expensive and the easiest to troubleshoot.
The trade-off: A fixed pressure high enough to prevent your worst events (often on your back, in REM sleep) can feel like more air than you need the rest of the night, and some people find exhaling against a constant pressure uncomfortable at first. Comfort features like exhalation relief, which briefly drops pressure as you breathe out, help a lot. A well-regarded fixed-pressure option is the Fisher and Paykel SleepStyle.
APAP: pressure that adjusts automatically
APAP (Auto-adjusting Positive Airway Pressure) is a smarter CPAP. Instead of one fixed number, your doctor sets a pressure range, and the machine continuously senses your breathing, flow limitation, and snoring, then raises or lowers pressure in real time. When you roll onto your back or enter REM and your airway needs more support, it pushes more; when you are breathing easily, it eases off.
Best for: First-time users, people whose pressure needs vary a lot by position or sleep stage, and anyone unsure of their exact ideal pressure. Because it only delivers as much pressure as the moment requires, many people find APAP more comfortable, and it can auto-titrate your needs over time. Most modern machines, including the popular ResMed AirSense 11 and the Philips DreamStation 2, can run in either fixed CPAP or auto APAP mode, so the hardware is often the same and the mode is a setting your provider chooses.
The trade-off: APAP machines cost a little more than pure CPAP units, and a small number of people find the constant micro-adjustments distracting. For most patients the added comfort outweighs both.
BiPAP: two pressures, inhale and exhale
BiPAP (Bilevel Positive Airway Pressure, sometimes written BiLevel or BPAP) delivers two distinct pressures: a higher IPAP when you breathe in and a lower EPAP when you breathe out. The gap between them makes exhaling much easier, because you are no longer fighting a wall of pressure every time you breathe out.
Best for: People who need high overall pressures (often above 15 cm H2O) that are uncomfortable to exhale against on CPAP or APAP; people who cannot tolerate CPAP despite comfort features; and certain medical conditions your doctor identifies, including some cases of central sleep apnea (where the brain intermittently fails to signal the breathing muscles), obesity hypoventilation, and some lung or neuromuscular disease. Advanced bilevel machines can also add a backup breathing rate for central events.
The trade-off: BiPAP is the most expensive category and is prescribed for specific reasons, not chosen for general preference. You will not typically start here unless CPAP or APAP has failed or your condition calls for it.
Side-by-side comparison
| Feature | CPAP | APAP | BiPAP |
|---|---|---|---|
| Pressure delivery | One fixed pressure | Auto-adjusts within a range | Two levels: higher in, lower out |
| Best first-line for | Stable pressure needs | Most new OSA patients | High pressure or exhale difficulty |
| Central sleep apnea | No | No | Sometimes (with backup rate) |
| Relative cost | Lowest | Moderate | Highest |
| Comfort exhaling | Good with pressure relief | Good | Best |
| Who chooses the mode | Sleep physician | Sleep physician | Sleep physician |
How your doctor actually decides
The choice is driven by your sleep study. An in-lab or at-home test measures your apnea-hypopnea index (AHI, the number of breathing events per hour), your oxygen levels, and whether events are obstructive or central. From there, a titration study or an auto-titrating machine determines the pressure that eliminates your events. If a single or auto-adjusting pressure controls your obstructive apnea comfortably, you get CPAP or APAP. If you need very high pressure, struggle to exhale, or have central or hypoventilation components, you move to BiPAP. This is why buying a machine off the internet and guessing at settings is a bad idea: the settings are the therapy.
The mask matters as much as the machine
Whichever machine you get, the mask is where success or failure usually happens. A leaking or uncomfortable mask sabotages even a perfectly chosen machine. The two broad options are a nasal mask, which covers or sits under the nose and is lighter and less claustrophobic (best if you breathe through your nose), and a full-face mask, which covers nose and mouth and suits mouth-breathers or people with congestion. Getting the fit right, with help from your equipment provider, does more for comfort than switching machine types.
Frequently asked questions
Can one machine do both CPAP and APAP? Yes. Most current auto machines run in either mode, so your provider can set a fixed pressure (CPAP mode) or a range (APAP mode) on the same device. BiPAP requires different hardware because it delivers two separate pressures.
Is APAP always better than CPAP? Not always. APAP is more adaptable and often more comfortable, but a well-set fixed CPAP works just as well for people with stable pressure needs and costs less. Studies find both control obstructive apnea effectively; the right one is whichever your physician sets for your data.
Do I need a prescription for any of these? Yes, in the United States all three are prescription devices. You need a diagnosis and a prescription that specifies the machine type and pressure, and reputable suppliers will ask for it.
Will insurance cover the machine? Often, yes, but coverage usually requires a documented diagnosis and proof that you are using the machine (adherence data the machine records automatically). Check your plan and ask your provider about compliance requirements before you start.
The bottom line
If your doctor has prescribed PAP therapy, the machine type follows from your sleep study, not from shopping preference. CPAP delivers one steady pressure and is the simplest and cheapest; APAP adjusts automatically and is the comfortable default for most new obstructive sleep apnea patients; BiPAP splits inhale and exhale pressures for people who need high settings or have central or hypoventilation issues. Focus your energy on getting the mask fit right and using the machine every night, then compare current devices in our CPAP and BiPAP machines hub and read the full CPAP buying guide before you talk settings with your provider.