Top pick
RVMattress.comSignature Hybrid
- Hybrid
- 13.25 in thick
- Soft / Medium / Firm
Sleep Foundation: Best Mattress Overall Read review
$1,865RV King - 72x80 · list priceSee price
Forest River Sierra 3990FL mattress size
Main bed72 × 80 inRV king
That's an RV king, 4 in narrower than a regular king (76 × 80 in). A regular king won't fit, so get an RV king in exactly 72 × 80 in.
About the RV king size →Forest River spec sheet, 2025.
Bunks44 × 74 in
Bunk. Forest River spec sheet, 2025.
Common RV bunk sizes →
Mattresses in 72 × 80 in
We may earn a commission when you buy through some of these links. It doesn't change which mattresses we list.
Best value
Mattress InsiderThe Sedona
- All-foam
- 5.5 in thick
- Firm
$40372" x 80" · list priceSee price
Reviewers' favorite
RVMattress.comAurora Luxe Cooling
- Hybrid
- 13.25 in thick
- Soft / Medium / Firm
Sleep Foundation: Best Mattress for Temperature Regulation Read review
$2,465RV King - 72x80 · list priceSee price
Best memory foam
Mattress InsiderElation Gel Foam
- Memory foam
- 6 in thick
- cushion firm
$65972" x 80" · list priceSee price
Best hybrid
RVMattress.comCopperFlex RV Hybrid
- Hybrid
- 10 in thick
- Medium-Firm
$1,065RV King 72x80 · list priceSee price
Best all-foam
RVMattress.comPlank Firm
- All-foam
- 10 in thick
- Firm / Extra Firm
Mattress Clarity: Best RV Mattress for Heavy People Read review
$1,532RV King - 72x80 · list priceSee price
Reviewer pick
HelixHelix Midnight
- Hybrid
- 11.5 in thick
- Medium Feel
Sleep Foundation: Best Mattress for Side Sleepers Read review
$1,489RV King · list priceSee price
Reviewer pick
Mattress InsiderPark Meadow Encased Coil II
- Hybrid
- 8 in thick
- cushion-firm
Sleep Foundation: Best Mattress for Pressure Relief Read review
$84972" x 80" · list priceSee price
Bunk mattresses in 44 × 74 in
Some bunks have a rounded corner, so trace yours before a custom cut. A thicker bunk mattress takes headroom from the bunk above.
Custom size
Mattress InsiderPark Meadow Encased Coil II
- Hybrid
- 8 in thick
- cushion-firm
Sleep Foundation: Best Mattress for Pressure Relief Read review
Made to 44 × 74 inGet a quote
The 3990FL floorplan
Forest River's 2025 3990FL floorplan.
Is this your 3990FL?
Check the year and length against your RV before you order.
| Year | Model | Length | Sleeps |
|---|---|---|---|
| 2024 | Sierra 3990FL | 43' 6" | – |
| 2025 | Sierra 3990FL | 43' 6" | – |
| 2026 | Sierra 3990FL | 43' 6" | 8 |
Other Sierra mattress sizes
Sources
- Forest River (forestriverinc.com), archived copy: https://web.archive.org/web/20250125101815/https://forestriverinc.com/rvs/sierra-fifth-wheels/3990FL/8265
- Forest River (forestriverinc.com), archived copy: https://web.archive.org/web/20260214224037/https://www.forestriverinc.com/rvs/sierra-fifth-wheels/3990FL/10194
- Forest River (forestriverinc.com), archived copy: https://web.archive.org/web/20250902211028/https://forestriverinc.com/rvs/ImageHandler/278583/2025_FW%20S25_3990FL%20copy%202.webp
- Forest River (forestriverinc.com), archived copy: https://web.archive.org/web/20251104223517/https://forestriverinc.com/rvs/sierra-fifth-wheels/3990FL/12043
- funtownrv.com: https://www.funtownrv.com/product/new-2026-forest-river-rv-sierra-3990fl-3455964-5
Questions
What size mattress is in the Forest River Sierra 3990FL?
The main bed is 72 × 80 in (Forest River spec sheet, 2025).
What size are the Forest River Sierra 3990FL bunk mattresses?
44 × 74 in (Forest River spec sheet, 2025).