Proto3000 supplies the Proto3000 Formlabs IBT Flex Resin as a low-durometer photopolymer for Formlabs low-force stereolithography systems. The product is used when a cured part must survive repeated flexural loading, compression, or snap-fit assembly without the localized tearing that occurs in rigid resins. The model designation is IBT Flex Resin; the material is sold in Formlabs-compatible cartridges and requires a resin-specific PreForm profile before printing. The formulation is distinct from Formlabs Flexible 80A and Formlabs Elastic 50A in its published durometer location and in the ratio of tensile strength to elongation. Because this is a third-party product, lot-specific data from the Proto3000 certificate of analysis is the controlling source for numerical specifications.

At incoming inspection, the cartridge should be conditioned in the printer bay until the resin reaches the temperature stated on the cartridge label. A cartridge placed directly from cold storage into a warm printer can generate higher meniscus viscosity at the build surface, which changes recoating thickness and can produce a visible horizontal boundary in the first layers. The cartridge should be inspected for settled solids or phase separation; if a clear supernatant layer is visible, the supplier’s documented rolling procedure should be used. Open cartridges should not be used beyond the supplier’s stated exposure interval, and unfiltered resin from a failed build should not be returned to the cartridge because partially polymerized particulate will create point defects in subsequent layers.

What Durometer Boundary Separates IBT Flex From Existing Formlabs Elastomeric Resins?

Durometer comparisons in flexible photopolymers are meaningful only when the test specimen is post-cured under the same UV dose and thermal history as the production part. Under ASTM D2240, Formlabs Flexible 80A is published at 80A and Formlabs Elastic 50A at 50A. The IBT Flex Resin is positioned by Proto3000 in a different elastomeric region; the exact Shore value is not to be inferred from the product name and must be taken from the current certificate of analysis. For design purposes, Shore hardness alone is insufficient because two materials with similar durometer can exhibit different tensile strength and tear behavior under ASTM D638-14 and ASTM D624. The table below shows the comparative published values for Formlabs resins; the IBT Flex column is intentionally lot-specific because no verified third-party numerical datasheet was available for citation at the time of writing.

Published data for this specific IBT Flex configuration is limited; engineers should not transfer Formlabs published tensile or tear values into IBT Flex validation documents. The supplier’s certificate of analysis remains the only acceptable source for batch acceptance. Where a production process is governed by ISO 9001 or ISO 13485, the certificate should be stored with the batch record and linked to the printer log, the post-cure cycle, and the inspection method. First-article validation on the actual printer is required because lot-to-lot changes in photoinitiator concentration can shift the working curve without changing the liquid resin appearance.

A durometer reading taken on a part thinner than 6.0 mm can reflect the hardness of the underlying support table rather than the resin. ASTM D2240 requires a specimen thickness sufficient to prevent substrate interference; for soft elastomers, the supplier’s certificate may specify a multi-layer specimen. The Shore A scale is also nonlinear at the low and high ends, so a difference of 5A at 80A is not equivalent to the same interval at 50A. Designers who select a flexible resin for dynamic fatigue should compare the full stress-strain response under ASTM D638-14 and the tear strength under ASTM D624 before durometer alone.

Formlabs Flexible 80A is generally selected for stiffer elastomeric parts such as tubing clips and snap-fit closures where tear strength and abrasion resistance are more important than low-force conformability. Formlabs Elastic 50A is selected for soft cushioning and seals that must fill a large gap or tolerate surface irregularities. The IBT Flex Resin is positioned for applications that require an intermediate balance; the actual dissimilarity with Formlabs materials is demonstrated by the lot-specific data. A production line that currently uses Flexible 80A should not assume that IBT Flex can be substituted without changing the offset allowance in a mating assembly.

Washing low-durometer photopolymers requires a solvent exposure limit different from rigid resins. Isopropyl alcohol at 99% or higher concentration is commonly used, but an over-long wash can swell the crosslinked network and leave a tacky surface that cannot be fully recovered by post-cure. The solvent interval shown in the IBT Flex technical data sheet is a maximum, not a target. After washing, residual solvent retained in blind holes, undercuts, or compression ribs plasticizes the cured surface; the local Shore A value can drop below the bulk reading. Post-wash drying should be confirmed by mass loss or by visual absence of solvent sheen on a matte surface before UV post-cure begins.

Post-Cure Uniformity and the Compression Set Boundary

Compression set is the more sensitive indicator of under-cure for this class of material. A part that reaches the expected Shore A value may still exhibit unacceptable compression set under ASTM D395 Method B when the post-cure dose is non-uniform or when the UV chamber’s lamp output has degraded. Post-curing in a Form Cure or equivalent 405 nm chamber should be validated for the largest production part geometry, not only for a flat coupon. The edges of a thick rubber-like block receive different photon flux than the center; this gradient produces a softer core that can relax under sustained load. Radiometric verification at 405 nm should be recorded before each batch, and the post-cure time and temperature should be treated as dimensional controls.

Under-cured IBT Flex parts retain unreacted methacrylate groups, which can continue to crosslink during storage and cause late shrinkage. Over-curing, by contrast, reduces elongation at break and increases the probability of notched tear propagation from support marks or surface scratches. Therefore the post-cure cycle is not a generic step; it must match the supplier’s stated process and the final part thickness. Parts above 5 mm may require reduced layer thickness or extended gentle cure rather than a single high-intensity exposure, depending on the certificate of analysis.

For a Form Cure chamber, the nominal emission at 405 nm and the heated platform should be checked against an independent radiometer before each batch; lamp aging and reflectors can generate greater than 15% irradiance drift across the cavity. Large parts should be rotated if the chamber has no rotating platform. Under a non-uniform cure, one face of a gasket may develop a harder surface while the opposite face remains tacky; this condition is frequently misidentified as under-washing when it is actually under-cure. Process engineers should record post-cure temperature, duration, and peak irradiance in the batch record. If the part shows compressive set greater than the value specified in the certificate after a standard cycle, the post-cure cycle should not be extended without first checking the UV lamp output and the part’s residual solvent content.

Compression set is measured by deflecting a cylindrical specimen to a fixed strain under ASTM D395 Method B, generally at 23 °C or 70 °C for the specified aging period. A part with high compression set may continue to seal after short-term service but loses contact force after thermal cycling. For IBT Flex, the acceptance threshold is lot-specific. When the application requires 24 h continuous compression at 70 °C, the material should be tested in the final production geometry rather than on a standard plaque because internal voids and layer boundaries influence recovery. Published data for this specific configuration is limited; internal validation is required.

Support contact on low-durometer surfaces differs from rigid photopolymer support removal. The tear strength of the material is the limiting parameter for support tip size and spacing. Coarse support tips can initiate catastrophic tears during manual removal because the cured support is often stiffer than the surrounding low-crosslink network. The part should be oriented so that flexural surfaces are not parallel to the build platform in high-support-density regions. If a tear starts at a support tip, the part should be discarded or evaluated under ASTM D624 because the notch sensitivity of elastomeric photopolymers is high. Published data for this specific configuration is limited, so first-article tests should include notched tear specimens produced on the same build platform as the production geometry.

Finishing of IBT Flex parts proceeds with sharp side cutters or a scalpel, but the cut line should be located away from functional flexural hinges. Sanding or grit blasting is generally not recommended for low-durometer parts because abrasive media can open surface pores and create tear initiation sites. If surface smoothing is required, a brief solvent wipe may be used only if the solvent is listed in the supplier’s post-processing guide. All finishing should be performed before post-cure whenever possible; post-curing after sanding can seal the surface but will not repair microtears created during finishing.

Adhesion of elastomeric builds to the build platform is often higher than the tear strength of the green part. The part should be removed with a plastic scraper or the printer’s recommended tool. Aggressive metal blade removal can create subsurface tears that remain invisible until cyclic loading. The build platform should be inspected for residual cured islands after every printing campaign; a small island in the platform surface produces a stress concentration that can reroute the first layer and change the thickness of each subsequent layer. Calibrating the platform with the manufacturer’s routine is not optional after a flexible resin build.

Before post-cure, the printed part is in a green state with a lower tensile strength and higher elongation than the final cured network. Handling a green flexible part can permanently stretch or distort thin fins and sealing lips. If the part is allowed to rest under its own weight before post-cure, the unsupported overhangs may creep. The time between printing and post-cure should be controlled as a process variable. A lot that is printed at the end of a shift and left overnight in the build chamber may not have the same dimensions as a part that is washed and cured within the supplier’s stated interval.

When Viscosity Drift in a Third-Party Cartridge Disrupts Night-Printing

Cartridge rheology is a production risk for unattended builds. The IBT Flex Resin certificate lists viscosity at 25 °C; significant upward drift from the certified value is often caused by low room temperature, moisture ingress, or partial polymerization after overwarm storage. In a low-force stereolithography system, increased viscosity changes recoating speed and can leave thin streaks or uncoated zones. If the printer firmware does not contain a calibrated viscosity compensation curve for third-party resins, the operator must control the room temperature and cartridge conditioning time rather than relying on automatic settings. A deviation greater than the tolerance stated by Proto3000 should trigger a pre-production check of the cartridge, tray, and build chamber temperature.

On a large-format Form 3L build, temperature gradients across the resin tray are more pronounced than on smaller platforms; a tray positioned near a draft or cooling vent can show variable part gloss and layer banding. Batch logs from production-scale stereolithography commonly record room temperature at start, mid-print, and end, along with the cartridge lot and the elapsed time since opening. When a new lot of IBT Flex Resin is introduced, the part dimensions and durometer should be re-established on a small validation coupon before the full build volume is committed. This is a boundary condition of third-party resin use in closed-loop Formlabs hardware.

On a production line running a Form 3L with multiple cartridges, lot-to-lot variation in flexible resin can appear as a shift in the support removal force rather than a visible change in printed appearance. That force is an indirect measure of crosslink density and solvent retention. A sudden increase in support removal force can indicate that the resin is over-curing in the green state; a sudden decrease can indicate under-cure or solvent swelling. Process engineers should log this qualitative force because it is often the first indication of a cartridge that has drifted outside the supplier’s acceptance range.

Validating a Third-Party Resin in ISO 13485 Environments

If the printed part is intended for medical device prototyping or production, the IBT Flex Resin must be supported by the supplier’s documentation for biocompatibility, not by assumption. The absence of a specific ISO 10993 test result in the certificate means the material has not been validated for patient-contact use. In an ISO 13485 environment, the resin lot, printer serial number, PreForm profile revision, wash solvent batch, and post-cure cycle are all part of the device history record. The product can be used for tooling and fixtures within a regulated facility without patient-contact validation, but the tooling must not shed particles into the final device. Cleaning validation of soft elastomeric fixtures is more complex than for metal fixtures because the resin surface can retain process fluids in micropores.

For industrial production not governed by medical standards, the principal compliance anchors are the resin’s safety data sheet and the applicable workplace exposure limits for cleaning solvents. The cartridges should be disposed of according to local cured and uncured photopolymer waste rules. The safety data sheet gives the flash point and viscosity, but the operator should also verify that the wash solvent drying area is ventilated below the occupational exposure limit. These compliance points are often missing from a basic product introduction and should be included in a production risk assessment.

Typical production uses for IBT Flex Resin include soft-touch tooling inserts, sealing gaskets that must recover after repeated compression, vibration-isolation mounts, and protective covers with snap-fit closures. In sealing applications, the compression set boundary under ASTM D395 and the tear strength under ASTM D624 control the service life more directly than Shore hardness. In snap-fit covers, the flexural hinge design should avoid sharp internal corners; stress concentrations at these corners reduce the number of cycles before tear propagation. The selection of a flexible photopolymer should be based on the complete post-cured stress-strain curve, not on the liquid resin appearance or the marketing durometer range.