SAE felt grades explained: which wool felt fits your part
- SAE J314 covers 11 common wool felt grades, from F-1 (95% wool, hardest) to F-26 (45% wool, softest).
- Grade sets wool content, weight and tensile strength; thickness is ordered separately.
- The standard is still current: SAE reaffirmed J314 in September 2022.
SAE felt grades are wool felt specifications from SAE J314. Each grade fixes minimum wool content, weight per square yard at 1 inch thick and minimum tensile strength. F-1 is the densest and strongest. F-26 is the softest. Lower F-numbers suit seals and wear parts; higher numbers suit padding and sound damping.
What does an SAE felt grade tell you?
An SAE felt grade tells you what the wool felt is made of and how hard it is. It does not tell you the thickness.
Every grade in SAE J314 carries four numbers that matter on a drawing: minimum wool content, weight in pounds per square yard at 1 inch (25.4mm) thick, minimum tensile strength and elongation. The rest of the felt is other fiber, usually a synthetic. White grades such as F-1, F-5 and F-10 are 95% wool, which is why they hold oil well and wear slowly. Gray grades trade some wool for cost.
So “F-1, 1/4 inch” is a complete call-out, while “F-1” alone is not. When you send a drawing for custom felt washers, put the grade and the finished thickness in the same note.
How do the SAE grades compare?
The first table ranks the grades by wool content and strength. Values are SAE J314 minimums.
| Grade | Min wool content | Min tensile strength |
|---|---|---|
| F-1 | 95% | 500psi (3.4MPa) |
| F-2 | 90% | 500psi (3.4MPa) |
| F-3 | 85% | 400psi (2.8MPa) |
| F-5 | 95% | 400psi (2.8MPa) |
| F-6 | 87% | 275psi (1.9MPa) |
| F-7 | 80% | 250psi (1.7MPa) |
| F-10 | 95% | 225psi (1.6MPa) |
| F-11 | 87% | 200psi (1.4MPa) |
| F-13 | 75% | 75psi (0.5MPa) |
| F-15 | 55% | 75psi (0.5MPa) |
| F-26 | 45% | Not rated |
The second table shows how dense each grade is. The metric density is our conversion of the published weight, so treat it as a guide rather than a spec limit.
| Grade | Weight at 1in thick | Approx. density |
|---|---|---|
| F-1, F-2 | 16.0lb/sq yd | 0.34g/cm³ |
| F-3 | 15.6-16.0lb/sq yd | 0.33-0.34g/cm³ |
| F-5, F-6, F-7 | 12.24lb/sq yd | 0.26g/cm³ |
| F-10, F-11, F-13, F-15 | 8.48lb/sq yd | 0.18g/cm³ |
| F-26 | 7.20lb/sq yd | 0.15g/cm³ |
Which SAE grade should you choose?
Choose an SAE felt grade by what the felt part has to survive, then pick the cheapest grade that survives it.
- F-1, F-3: impact, abrasion and repeated compression. Typical parts are shaft seals, bumpers, bushings and vibration mounts. F-1 is the usual choice for bearing and shaft felt seals and for felt lubrication pinions on rack drives.
- F-5, F-7: medium duty. Grease retainers, dust shields, spacer strips and oil wicks. F-7 does the F-5 job where some wear is acceptable.
- F-10, F-11: softer but still high wool. Oil retention under light load, gas and air plug filters.
- F-13, F-15, F-26: padding, anti-squeak strips, chassis spacers and sound damping, where strength hardly matters. These are common in felt gaskets for anti-rattle jobs.
One trap catches buyers often. A softer grade does not seal better just because it compresses more. On a rotating shaft, a low-density felt packs down and opens a gap within weeks, while F-1 keeps a steady lip pressure through wear and small misalignment.
Felt seals in general work the same way: they keep a constant sealing pressure despite wear, end play and minor misalignment, as long as the felt is dense enough to spring back.
How do you pick a grade from the way a part fails?
Start from the failure you want to avoid, not from the grade list.
Each way a felt part can fail points to a lowest SAE grade that usually holds up. Anything softer tends to fail the same way, only sooner. Anything harder works too, but you pay for strength the job does not use.
| Failure to avoid | Lowest grade that usually holds | What a softer grade does |
|---|---|---|
| A seal or wiper loses contact as it wears | F-1, or F-5 on light duty | Packs down and opens a gap |
| A bumper or mount flattens under repeated knocks | F-1 or F-3 | Loses thickness and works loose |
| A wick or grease retainer runs dry | F-5 or F-7; F-10 under light load | Lower-wool grades hold less oil |
| A pad or spacer squeaks against trim | F-13 to F-26 | Softer is fine here; harder only adds cost |
What temperature can SAE wool felt handle?
All SAE wool felt grades work from -80 to 200°F (-62 to 93°C). Above that, wool starts to degrade, so hot zones need a synthetic such as needle-punched polyester felt, which runs continuously at up to 300°F (149°C). SAE wool felt also recovers 99% of its thickness within one minute after a 10% deflection, which is why wool felt keeps sealing as it wears.
Is SAE J314 still a current standard?
Yes. SAE last reaffirmed J314, “Felts – Wool and Part Wool”, in September 2022 (J314_202209) and describes it as stable technology. Drawings that cite older revisions, such as J314_199405, still point to the same grade names.
SAE felt grade FAQ
Is F-1 felt the same as 100% wool felt?
No. F-1 needs at least 95% wool, and it also sets a weight and a minimum tensile strength of 500psi. “100% wool” only describes the fiber. It says nothing about density or strength, so a soft 100% wool felt can still fall short of F-1.
Can I swap F-5 for F-1 to cut cost?
Only where the part sees little impact or abrasion. F-5 is 95% wool like F-1 but about a quarter lighter, so it wears faster under load.
Does the grade include thickness?
No. Thickness is specified separately, for example F-1 at 1/8in (3.2mm) or 1/2in (12.7mm).
Which grades are white and which are gray?
F-1, F-5 and F-10 are white. F-3, F-6, F-7, F-11, F-13, F-15 and F-26 are gray. F-2 can be any color except gray or black.
What is F-3 felt?
F-3 is a gray SAE wool felt with at least 85% wool and 400psi (2.8MPa) minimum tensile strength. It is nearly as dense as F-1 and suits vibration mounts and bumpers where white felt is not needed.
What is F-5 felt?
F-5 is a white SAE wool felt with at least 95% wool, the same as F-1, but about a quarter lighter at 12.24lb/sq yd per inch of thickness. It suits grease retainers, dust shields and medium-duty seals.
What is the highest quality felt?
In the SAE range, F-1 is the densest and strongest wool felt, with 95% wool and 500psi (3.4MPa) tensile strength. It is not always the right choice, because a softer grade does many jobs as well for less money.
Not sure which grade your part needs?
Send the drawing and the working conditions. An engineer will suggest a grade and quote custom felt parts to your drawing.