Fits checked Oct 1, 2026 · How we check
Filter Fit Finder
Menu

Alen · air purifier

Alen BreatheSmart 45i replacement filter

Use part B4-Pure. Replace every 6-12 months.

The filter that fits

Maker lists this model

Alen 45i & FLEX Filter, Essential (Pure)

BreatheSmart 45i & FLEX HEPA Filter, Essential (Pure)

Part number
B4-Purealso sold as FL40-Pure
How many
1 per unit
How often
Replace every 6-12 months
Buy 45i & FLEX Filter, Essential (Pure) on AmazonManufacturer page

Opens an Amazon search for Alen 45i & FLEX Filter, Essential (Pure) B4-Pure. Check the listing says B4-Pure.

See the sources

Look-alike models that take a different filter

The BreatheSmart 75i looks similar but takes the larger B7 filter; the 45i filter does not fit it.

Other genuine options from Alen

Variants and kits the maker sells for this model. Same fit, different media or packaging.

  • BreatheSmart 45i & FLEX HEPA Filter, Advanced (Fresh), formerly B4 Fresh
    F10017 · Find on Amazon
  • BreatheSmart 45i & FLEX HEPA Filter, Ultimate (Odor), formerly B4 Odor
    F10014 · Find on Amazon

Sources

High confidence: the manufacturer names this exact model on a live page. Each line is the page we read and the day we read it.

  • Which filter fits alen.com Maker's own page checked Oct 1, 2026
    BreatheSmart 45i & FLEX HEPA Filter ... Q: Will this filter also fit in Breathsmart Flex unit? A: Yes. The BreatheSmart 45i and BreatheSmart FLEX share the same filters.
  • How many web.archive.org Maker's archived page checked Oct 1, 2026
    Page for the BreatheSmart 45i (per its URL): Remove the used filter by pulling out on the ribbon loop ... Take the new filter out of the plastic bag and insert it into the purifier with the ribbon loop facing outward (archive.org copy of 2025-10-09)
  • How often alen.com Maker's own page checked Oct 1, 2026
    Purifier includes filter rated for: 6-12 months
  • What's in it alen.com Maker's own page checked Oct 1, 2026
    All of our filters come with a Prefilter attached. On the BreatheSmart 45i filters, the prefilter is the black-mesh attachment with Velcro on the front of the filter.
  • Other genuine options alen.com Maker's own page checked Oct 1, 2026
    (Formerly B4 Fresh) ... (Formerly B4 Odor)
Show all 9 sources

Which filter fits

  1. alen.com Maker's own page checked Oct 1, 2026
    BreatheSmart 45i & FLEX HEPA Filter ... Q: Will this filter also fit in Breathsmart Flex unit? A: Yes. The BreatheSmart 45i and BreatheSmart FLEX share the same filters.
  2. alen.com Maker's own page checked Oct 1, 2026
    Our entry-level filter. Features a medical-grade HEPA filter that captures 99.9% of airborne dust, viruses, and allergens. (Formerly B4 Pure)
  3. alen.com Maker's own page checked Oct 1, 2026
    BreatheSmart 45i & FLEX HEPA Filter variants: Essential (Pure) F10016; Advanced (Fresh) F10017; Ultimate (Odor) F10014
  4. web.archive.org Maker's archived page checked Oct 1, 2026
    4 Filter options: Pure, Fresh, Odor, and VOC/Smoke | BreatheSmart FLEX & 45i filters are compatible (archive.org copy of support.alen.com, 2025-09-05; live page returns 403)
  5. web.archive.org Maker's archived page checked Oct 1, 2026
    Breathesmart FLEX HEPA Air Filter: B4-Pure / FL40-Pure (archive.org copy of 2023-06-03)

How many

  1. web.archive.org Maker's archived page checked Oct 1, 2026
    Page for the BreatheSmart 45i (per its URL): Remove the used filter by pulling out on the ribbon loop ... Take the new filter out of the plastic bag and insert it into the purifier with the ribbon loop facing outward (archive.org copy of 2025-10-09)

How often

  1. alen.com Maker's own page checked Oct 1, 2026
    Purifier includes filter rated for: 6-12 months

What's in it

  1. alen.com Maker's own page checked Oct 1, 2026
    All of our filters come with a Prefilter attached. On the BreatheSmart 45i filters, the prefilter is the black-mesh attachment with Velcro on the front of the filter.

Other genuine options

  1. alen.com Maker's own page checked Oct 1, 2026
    (Formerly B4 Fresh) ... (Formerly B4 Odor)