TL;DR — Only nylon and silk have ever been measured as finished dental floss: in the single study that tested both, nylon floss reached 49.28 ± 9.07 MPa tensile strength, silk was not statistically different from it, and silk was the roughest of the four materials tested (Ra 0.3035 ± 0.0254 µm versus nylon's 0.10 ± 0.022 µm). PLA floss has never been characterized in a peer-reviewed study at all — the numbers quoted for it come from lab-spun PLA yarn, where disintegration required 58 °C in an industrial-composting test and did not occur at 28 °C over 14 weeks. On disposal, all three end up in the same place: landfill.
That box is not a compressed version of a larger literature — it is close to the whole of it. One peer-reviewed comparison has ever put finished flosses on the same test rig, PLA floss has never been characterized at all, and every degradation number in circulation was generated far from a bathroom bin. The honest state of the evidence is thinner than the category's marketing implies; what follows is what the few real measurements show, and where the gaps sit.
The three materials on measured criteria
| Criterion | Nylon (multifilament) | Silk (Bombyx mori) | PLA (corn-derived) |
|---|---|---|---|
| Tensile strength, measured on finished floss | 49.28 ± 9.07 MPa | Not significantly different from nylon | Never measured in floss form |
| Surface roughness (Ra) | 0.10 ± 0.022 µm | 0.3035 ± 0.0254 µm — roughest of four tested | Not measured |
| Filament structure | Many filaments wound into thread | Many filaments wound into thread | Typically multifilament; no published characterization |
| In vitro abrasion against human enamel | No significant difference between materials | No significant difference | Untested |
| Force needed to pass tight contacts | Measured; higher than PTFE | Untested | Untested |
| Filament breakage after use | Documented by electron microscopy | Same structure, same expected mechanism, untested | Untested |
| Where it actually goes after use | Landfill | Landfill | Landfill |
| Accepted by municipal composting | No | No — and wax coatings are separately excluded | No |
| Degradation conditions with a published number | None published | Enzymatic, in laboratory biomaterial studies only | 3 weeks at 58 °C (ISO 20200); none at 28 °C in 14 weeks |
| Typical US retail cost per meter | ~$0.04 | ~$0.17–0.20 | Rarely published with spool length |
Sources for each row are linked in the sections below. Rows marked "untested" are not hedges — they are the actual gaps.
Where the mechanical numbers come from
The one study that compares floss materials head to head under a single method is by Zhongjin Huang, Jonathan M. Broadbent and Joanne Jung Eun Choi, published in Biomaterial Investigations in Dentistry in 2023. They tested four commercial flosses — nylon, silk, PTFE and UHMWPE — for tensile strength, surface roughness, enamel abrasion and user preference.
Figure 1 — Tensile strength of finished floss, as measured
Three findings from it matter more than the headline numbers.
First, the tensile figures are calculated across each thread's whole cross-section, so they describe the product, not the polymer. PTFE's very low 11.78 MPa reflects a flat, sheet-like ribbon geometry, not a thread that snaps in your hands.
Second, the block-on-ring abrasion test found no significant difference between the four materials against human enamel. Whatever separates these materials, measurable enamel wear in that test was not it.
Third — and this is the finding the category tends to skip — a clear majority of participants disagreed that any of the four flosses frayed or shredded during use. The "nylon shreds" claim that appears in almost every plastic-free floss roundup did not reproduce in the one study that asked users directly.
Only four products were tested, one per material. Material and brand cannot be separated in that design. The preference arm had 16 participants over eight days per floss. Treat it as the best available comparison, not as settled fact.
Nylon: strong, rougher than PTFE, and the only one with fraying imaged
Nylon multifilament is the reference case because it is the most tested. Its 49.28 MPa is four times PTFE's figure and about a quarter of UHMWPE's 194.18 MPa.
The mechanism behind fraying was imaged directly by Adrian K. Stavrakis, Sanja Kojić, Bojan Petrović and colleagues in Materials (2022). Using scanning electron and optical microscopy on flosses before and after real use, they found clearly fractured filaments in a flat, compacted floss, while the two genuinely twisted multifilament threads showed only minor visible structural damage. One flat sample went from roughly 50 % elongation at break when new to roughly 150 % after use — the internal structure was destroyed even though breaking force fell by only about 10 N.
So fraying, where it occurs, is filament rupture rather than surface wear — and in that dataset it tracked construction more than chemistry: the flat, compacted floss fractured while the conventional twisted threads largely held together. Silk and most PLA flosses share that twisted multifilament construction; neither has been imaged after use, but the same mechanics would be expected to apply.
On glide, the closest direct measurement is still Christof E. Dörfer and co-authors in the Journal of Periodontology (2001), who used strain gauges to record insertion and removal force through 14 interproximal contacts in 27 participants and found that PTFE flosses passed strong proximal contacts with less force than nylon. Silk and PLA were not in that study. Nobody has repeated it with them.
Silk: the roughest of the four, and the disposal claim that outruns the data
Silk floss measured statistically the same tensile strength as nylon and the highest surface roughness of the four materials. Roughness is a plausible explanation for the recurring subjective complaint that silk feels like string between tight teeth, though roughness and perceived harshness were not formally correlated.
The material's reputation rests on how it breaks down. Silk fibroin is degraded enzymatically — a protocol paper from David Kaplan's group at Tufts University in Nature Protocols notes that silk degradation is mediated by proteases, through surface erosion, in studies running up to 12 weeks.
Read the context before repeating that. Those experiments are implant and tissue-engineering work, run in vitro with purified protease XIV. They are not compost, soil or landfill. The same source quotes raw Bombyx mori fiber at up to 740 MPa; the finished floss measured in the 2023 comparison came in around nylon's ~49 MPa. Use the floss number when discussing floss.
Commercial silk floss is also wax-coated, typically with beeswax or candelilla wax, and no peer-reviewed measurement of a coated finished product's degradation exists in either direction.
PLA: the material with the most confident marketing and the least data
There is no peer-reviewed study of PLA in dental floss form. What exists is fiber science.
Figure 2 — What was actually tested on PLA fibre
Mohammadreza Naeimirad and co-authors, publishing in Scientific Reports in 2025, melt-spun aliphatic polyester fibers and ran them through standardized disintegration tests. Under ISO 20200 industrial conditions at 58 °C the PLA fibers disintegrated within three weeks. Under home-composting conditions at 28 °C, the samples showed no disintegration up to 14 weeks. Under ordinary weathering at 25 °C and 65 % relative humidity, the yarn kept most of its mechanical properties over 80 days with roughly 8 % molecular-weight loss.
The reason is thermal, not biological. As Christine Lors, Pauline Leleux and Chung Hae Park set out in a 2025 Frontiers in Materials review, PLA's glass transition temperature is 58 °C for amorphous and 62 °C for semi-crystalline PLA — hydrolysis needs temperatures near that threshold. A backyard compost pile does not reach it.
Note also that "disintegration" under ISO 20200 means physical breakup on a sieve. It is not the same as full mineralization to CO₂ and biomass.
Disposal is where all three converge
Whatever the fiber, used floss follows the same route. One of the largest US organics programs, Hennepin County in Minnesota, lists dental floss among items not accepted in organics collection — and separately excludes wax and waxed products unless BPI-certified. Wax-coated silk is therefore caught twice.
Home composting is not the fallback either: in the largest independent citizen-science trial of the practice, UCL's Plastic Waste Innovation Hub gathered 1,307 usable home-composting results from UK households and found that 60 % of items certified "home compostable" still had clearly visible remains.
This is also where US law lands. The FTC's Green Guides state that an unqualified degradable claim is deceptive for items entering the solid waste stream if they do not completely decompose within one year after customary disposal — and the guides say outright that landfills, incinerators and recycling facilities do not provide those conditions. Given where floss customarily goes, an unqualified degradation claim about any of these three materials is difficult to support.
What the research has not settled
- No published tensile, roughness, glide or abrasion measurement of PLA floss.
- No glide-force measurement for silk or PLA through tight contacts.
- No degradation measurement of any coated, finished floss product — silk or PLA.
- No credible figure for microplastic release from floss. A 2025 review in Materials on micro- and nanoplastics in dentistry concludes the quantitative data are sparse; treat any specific particle count you see as unsourced.
- No study separating material effects from brand effects, because every comparison so far used one product per material.
When plastic-free — or reusable — is the wrong call
Two findings should temper the whole category.
First, floss may not be the right tool for you at all. The American Dental Association's own guidance states that the choice of interdental device depends on patient anatomy — floss for tight spaces, interproximal brushes for periodontitis or more open spaces. If you have symptoms, bleeding, or existing gum disease, that is a conversation for your dentist, not a materials article.
Second, the environmental ranking does not favor floss: in the life-cycle comparison of eight interdental products led by Rawan Abed with Paul Ashley and Brett Duane in the Journal of Clinical Periodontology (2023), floss picks ranked worst and a bamboo interdental brush best — so if a brush suits your mouth, it beats every floss in that study, in any material.
And the underlying clinical evidence is weak. The Cochrane review led by Helen Worthington at the University of Manchester pooled 35 randomized trials with 3,929 adults and reported that the evidence was low to very-low certainty and observed effect sizes may not be clinically important.
The verdict
If the criterion is measured performance, nylon and silk are close and PLA is unmeasured — pick on feel and price, and note that silk costs about five times more per meter for no measured mechanical advantage. If the criterion is what happens after disposal, none of the three has a verified answer under real US conditions, and the material that most loudly claims one has the least data behind it. If the criterion is total footprint, the biggest single lever is not the thread at all — it is whether there is a disposable plastic handle attached to it.
The honest summary: the fiber matters less than the format, and less than whether the tool fits your mouth.
Figure 3 — LastFloss
