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CPAP Clarity
PublishedUpdated16 min read
By Brian C., CPAP user since 2023Editorial standards

Best SD Card for Your CPAP (2026 Guide)

Which SD card works with your CPAP? Card type, size, format, and top picks for every brand. ResMed, BMC, Luna G3, and more.

The best SD card for a CPAP is the one it came with. For a replacement, the right card depends on your machine, and the maker's own card from your supplier is always the safe choice. An AirSense 11 takes an SDHC card like ResMed's own 4GB card, so a name-brand one of 32GB or less is the same type. An S9 needs ResMed's own 1GB or 2GB card, and a Löwenstein prismaLINE tops out at 8GB. The table below covers each machine.

Which Card Each Machine Takes

This is what each maker's own documents say. Where a maker publishes nothing, the card from your supplier is the safe choice.

MachineWhat the maker saysWhat to use
ResMed AirSense 11ResMed's own Air 11 SD card (part 39228) is a 4GB SDHC cardResMed's card from your supplier, or a name-brand full-size SDHC card of 32GB or less
ResMed AirSense 10, AirCurve 10 and AirStart 10ResMed's device FAQ says SDHC cards don't work; the AirStart 10 takes the same card as the AirSense 10ResMed's card from your supplier
ResMed AirCurve 11No card spec publishedResMed's card from your supplier
ResMed S9ResMed supplies 1GB and 2GB cards and says SDHC cards do not work in the S9A 1GB or 2GB ResMed card from your supplier, never SDHC
ResMed AirMiniNo SD cardNothing to buy; its data comes through the app
Philips DreamStation, DreamStation 2Philips' own cards hold 8GB, and both machines take the same kind of cardPhilips' card from your supplier
Löwenstein prisma SMART and SOFTA brand-name card between 2GB and 32GBA name-brand full-size card in that range
Löwenstein prismaLINE (prisma20A and its siblings)A brand-name card between 256MB and 8GBLöwenstein's card, or a name-brand card of 8GB or less
BMC E-20A and G3 A20Both manuals say to get the card from BMC ("contact the manufacturer" / "contact BMC")BMC's card from your supplier
React Health Luna G3Lists the card as an optional accessory, with no specA card from your supplier or React Health
YuwellNo manual found for the models CPAP Clarity reads; some Yuwell models take micro SDThe card it came with, or one from your supplier

Where the Card Goes

Most CPAP machines that CPAP Clarity reads take a standard, full-size SD card. That's the one that's 32mm x 24mm, the same size that was in digital cameras before everything went mirrorless. The exceptions are the ResMed AirMini, which has no card, and some Yuwell models, which take micro SD, so check yours.

Here's where the slot is, by brand:

ResMed (AirSense 10, AirSense 11, AirCurve 10, AirCurve 11 in all variants): the slot is behind a small cover on the left side of the machine, on the end opposite the humidifier water tub, when you face the screen (no need to remove the water chamber). Any of these machines record to a DATALOG folder structure with EDF signal files.

BMC (E-20A, G3 A20): on the E-20A the slot is on the side opposite the humidifier, on the same panel as the air filter. The G3 A20 is different: its slot sits on the humidifier side, so you slide off the water chamber to reach it. The machine writes proprietary binary files in a BMC folder. For a deeper look at the BMC data format, see the BMC E-20A and G3 A20 data guide.

React Health Luna G3: the slot is on the back panel. The Luna G3 takes a full-size SD card and writes its own binary format. Three different firmware versions exist with slightly different data layouts. See the Luna G3 data guide for details.

Lowenstein Prisma Smart: the slot is on the side of the machine. The Prisma writes JSON configuration, XML event files, and WMEDF signal files.

What Size to Get

Two constraints matter here: capacity and format.

Match the size to your machine. Cards larger than 32GB come formatted exFAT rather than FAT32, so we treat 32GB as the ceiling. Some machines want less: an S9 takes ResMed's own 1GB or 2GB card, and a Löwenstein prismaLINE takes 8GB or less. ResMed publishes no limit for its other machines.

Format: FAT32. That is the format SDHC cards use, per the SD Association. It is separate from the card's storage capacity. Cards 32GB and under ship from the factory pre-formatted as FAT32, so most people never need to think about this. More on formatting below.

Even a small card holds years of data. Here's roughly how much data each machine writes per night:

  • ResMed AirSense 11: approximately 2 to 5 MB per night
  • ResMed AirSense 10: approximately 5 to 15 MB per night (stores more detailed waveform data)
  • BMC E-20A / G3 A20: approximately 1 to 3 MB per night
  • React Health Luna G3: approximately 1 to 4 MB per night
  • Lowenstein Prisma Smart: approximately 2 to 6 MB per night

A 4GB card holds roughly 1 to 3 years of nightly data on any machine. An 8GB card doubles that. A 32GB card is essentially unlimited for practical purposes.

Do You Need a Manufacturer-Branded Card?

Not necessarily. ResMed's own Air 11 SD card is a 4GB SDHC card made by Delkin (part 39228, per its service manual), a standard card type, and Löwenstein only asks for a card from a brand-name maker. A name-brand, full-size SDHC card of 32GB or less is the same type of card. If your supplier will send a replacement under your plan, that's the simplest route.

ResMed's device FAQ says SDHC cards don't work with its machines. That page dates from the S9 and AirSense 10, and ResMed's own AirSense 11 card is SDHC, so we treat that line as out of date for the AirSense 11. ResMed's S9 pages say the same thing specifically about the S9, so for an S9 it stands. For an AirSense 10, use ResMed's card from your supplier. If your machine rejects a card, go back to the card it came with or ask your supplier.

One thing worth knowing: you don't need to create any folders manually before inserting a new card. The machine creates its own directory structure the first time it runs with a new card. ResMed creates a DATALOG folder, BMC creates a BMC folder, and so on. Just format it FAT32, insert it, and use the machine as normal. After your first night of therapy, the folders will be there.

How to Format Your Card

Most cards 32GB and under are already formatted FAT32 when you buy them. You only need to format a card yourself if:

  • You're reusing an old card that was formatted differently
  • The machine is throwing errors reading the card
  • You want to clear old data and start fresh

On Windows: Insert the card, open File Explorer, right-click the drive, choose Format. In the File System dropdown, select FAT32. Make sure "Quick Format" is checked and click Start.

On Mac: Open Disk Utility (Applications > Utilities > Disk Utility). Select the SD card in the left sidebar. Click Erase. In the Format dropdown, choose MS-DOS (FAT). Give it a name (anything works) and click Erase.

SD Association Formatter: The SD Association's official SD Memory Card Formatter is a free tool designed specifically for formatting SD cards. It handles edge cases (like cards with non-standard partition tables) that the built-in OS formatters sometimes struggle with. Download it for Windows (opens in new tab) or Mac (opens in new tab). If the built-in formatter above doesn't fix a stubborn card, try this tool before giving up on it.

One rule: don't manually create folders. The machine expects to create its own folder structure. If you create a DATALOG or BMC folder yourself, you may cause a conflict. Start with an empty, formatted card.

What to Avoid

A few things that cause trouble:

Cards larger than 32GB. They come formatted exFAT rather than FAT32. Löwenstein's prisma SMART manual tops out at 32GB, and ResMed doesn't publish a limit above that. Stay at 32GB or under, and lower where the table says so.

Micro SD with an adapter. Physically, a micro SD card with a full-size adapter can fit in the slot. The adapter introduces an extra contact point between the micro card and the machine's slot that a native full-size card does not have. ResMed says an adapter would likely work in an S9 but has not been shown to meet the IEC 60601-1 medical electrical safety standard, so it advises against one. Native full-size cards are inexpensive enough that there's no reason to risk intermittent contact issues.

Old WiFi SD cards. Eye-Fi and Toshiba FlashAir cards have been discontinued, and secondhand ones are a gamble. If you want your data to move off the machine without pulling the card, see automating CPAP imports with an EZShare card.

Our Top Picks: SD Cards

These three are name-brand, native full-size 32GB SDHC cards. They're the same card type as ResMed's own AirSense 11 card and fit Löwenstein's prisma SMART range. They are too big for an S9 (ResMed's own 1GB or 2GB card only) or a prismaLINE machine (8GB or less). For the other machines in the table above, the maker's card from your supplier is the safe choice.

Full-size 32GB SDHC cards for the AirSense 11 and prisma SMART

Editor's Pick

SanDisk Ultra 32GB SDHC UHS-I

The most widely available full-size 32GB SDHC card. 100MB/s read speed, UHS-I U1. Ships pre-formatted FAT32.

Prime Pick

Gigastone 32GB SDHC UHS-I

Full-size 32GB SDHC alternative with Prime shipping. UHS-I A1 V10, single card. Reformat to FAT32 if your machine needs it.

Most Reviewed

SanDisk Ultra 32GB Class 10 SDHC UHS-I

A second SanDisk full-size 32GB SDHC model, the highest-volume listing in this class. Class 10 UHS-I, native full-size.

All three cards are faster than what CPAP data transfer requires. The machine writes a few megabytes per night; even the slowest UHS-I card transfers that in under a second. Pick whichever is available at the best price.

Our Top Picks: SD Card Readers

To import your CPAP data into CPAP Clarity (or any analysis software), you need to connect the card to your computer. If your laptop has a built-in SD card slot, use that. Otherwise, pick the reader that matches your ports.

SD card readers by connection type

Best for Modern Laptops

USB-C SD Card Reader

Plugs into modern MacBooks, iPads (USB-C), and most Android phones. Supports full-size SD and microSD.

Best for Older Laptops

USB-A SD Card Reader

Plugs into older laptops and desktops with USB-A ports. Same functionality, typically a touch cheaper.

Best for Older iPhones

Apple Lightning SD Card Reader

Apple's official Lightning to SD Card Camera Reader. For iPhones and iPads with Lightning ports (iPhone 14 and earlier).

Android phone via USB OTG. Android phones with USB OTG support can connect to a USB-C card reader and access the SD card directly. Combined with a mobile browser, you can import your data from your phone. CPAP Clarity's folder import works in Chrome on Android.

iPhone and iPad. Current iPhones (iPhone 15 and later) use USB-C, so a USB-C SD card reader connects directly. Older iPhones with Lightning ports need the Apple Lightning reader listed above. CPAP Clarity's folder import works in Safari on iOS 17 and later. For a walkthrough of importing from cloud storage instead of a physical card, see our cloud storage import guide.

Once You Have the Card

The workflow is simple. Insert the card into your machine before going to sleep. Use your machine as normal. In the morning, remove the card and insert it into your computer using whichever reader applies to you.

Open CPAP Clarity and select the whole SD card folder when prompted. The import reads the entire directory structure and all session files automatically. You don't need to pick individual files. This works the same way regardless of whether your machine is a ResMed, BMC, Luna G3, or Lowenstein.

For a full walkthrough of the import process, see the CPAP SD card data guide. If you're new to CPAP Clarity, How to Use CPAP Clarity is the place to start. Once your data is in, How to Read CPAP Data explains what all the numbers mean. If the card isn't working, see our SD card troubleshooting guide.

Common Questions

Do all CPAP brands use the same SD card?

No. ResMed's S9 needs ResMed's own 1GB or 2GB card, while ResMed's own AirSense 11 card and Philips' own cards are SDHC (4GB and 8GB). Löwenstein's prisma SMART takes 2GB to 32GB, but its prismaLINE machines top out at 8GB. BMC asks owners to get the card from BMC. The table near the top of this guide covers each machine.

Can I use the same card in OSCAR and CPAP Clarity?

Yes. Both tools read the same files from the same SD card. You can import into CPAP Clarity, then plug the same card into OSCAR (or vice versa) without any issues. The files are not modified during import. If you're curious how CPAP Clarity compares to OSCAR, see our OSCAR alternative guide.

Does removing the card affect my therapy?

No. The SD card records data but plays no role in delivering therapy. Removing it (while the machine is off) does not change pressure, humidification, or any other setting. The machine will simply not record data on nights when the card isn't present.

Can I use a micro SD card with a full-size adapter?

We don't recommend it. The adapter adds a contact point between the micro SD card and the CPAP's SD slot that a native full-size card does not have. A native full-size 32GB SDHC card is inexpensive and avoids the risk of intermittent read errors from poor adapter contact. If you already have a micro SD with adapter and it's been working, there's no urgent reason to switch, but for a new purchase, go with a native full-size card.

What if my machine won't recognize the card?

First, make sure the card is 32GB or smaller. Cards above 32GB are formatted exFAT by default rather than FAT32. Second, try reformatting it as FAT32 using the steps in the formatting section above. If the OS formatter doesn't help, try the SD Association's free formatting tool for Windows (opens in new tab) or Mac (opens in new tab). Third, check that the card is fully seated in the slot. If none of that works, the card itself may be faulty: try a different card. For more help, see our SD card troubleshooting guide.

How often should I check my data?

That depends on where you are in your therapy. In the first few weeks, checking weekly gives you a sense of how your body is adjusting. Once therapy is stable, monthly is plenty for most people. If you're troubleshooting a problem (high leak rate, poor sleep quality), daily check-ins are worthwhile until the issue is resolved.

What do I do if the card is full?

Two options. First, you can reformat the card (FAT32, as described above) to wipe it and start fresh. Second, you can replace it with a larger card, up to 32GB. If you want to keep your historical data, copy the entire card contents to your computer before reformatting or swapping cards.

Can I leave the card in the machine all the time?

Yes, and most people do. The card is only accessed when the machine is writing data at the end of a session. Leaving it in is fine. Just remember to remove it when you want to import your data.

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