Carrying-case selection is driven by payload mass, drop height requirement, ingress protection target, and unit volume: the five mainstream shell technologies — custom EVA, vacuum-formed, blow-molded, plastic-injected, and soft sewn — are listed side-by-side in current custom-case OEM literature, each with distinct density, impact-absorption, and tooling-cost profiles [S1].
For buyers comparing off-the-shelf enclosures to custom builds, the decision pivots on three numbers: peak drop height in cm, target unit cost in USD per piece, and minimum order quantity (MOQ). Custom medical-device case suppliers such as Shell-Case document a 20-year track record across medical, electronics, optics, and industrial measuring instruments, and they list EVA, vacuum forming, blow molding, plastic injection, soft sewn, and advanced bonding as their core process set [S1].
Shell Construction: Five Process Families and Their Spec Bands
Custom EVA cases (ethylene-vinyl acetate foam, typically 38–75 Shore C, density 80–200 kg/m³) absorb impact through closed-cell foam geometry and dominate low-volume, high-shock duties such as diagnostic instruments and hand-held optics [S1].
Vacuum-formed cases use heated thermoplastic sheet (commonly ABS or Kydex at 1.5–4.0 mm gauge) drawn over a single-side mold, making them economical for runs of roughly 50–500 units where wall uniformity and cosmetic finish matter more than extreme drop survival [S1].
Blow-molded cases are produced from HDPE or PP parisons, yielding hollow double-wall shells that reach typical wall thickness of 2.5–6 mm and deliver high rigidity-to-mass ratios, which is why the format is standard for power-tool kits and portable industrial measurement gear [S1].
Plastic-injected cases use injection-molded thermoplastics (ABS, PC, PA66) with insert-molded bosses and hinge features, fitting medium-to-high volumes (1,000+ units) where repeatability of latches, hinges, and gasket grooves is non-negotiable [S1].
Soft sewn cases pair woven outer shells (ballistic nylon 500D–1000D, polyester 600D) with foam-padded internals and welded or stitched seams, and they remain the lowest-weight option for field sales kits and wearables where flexibility outweighs rigid impact protection [S1].
Decision Criteria: Drop, IP, Mass, Tooling, MOQ
Drop height is the first filter: under 1.0 m typical desk-height handling, EVA shells at 30–50 mm wall absorb sufficient energy for handhelds under 2 kg; above 1.5 m or payloads above 5 kg, blow-molded or injection-molded cases with engineered rib geometry are the realistic path [S1].
Ingress protection bands map tightly to construction: soft-sewn and EVA cases without welded seams typically achieve IP54 at best, while injection-molded shells with continuous gaskets (TPE or silicone cord) routinely reach IP65–IP67 in documented industrial carrying-case offerings [S1].
Mass budgets matter in wearables and field sales kits — a soft sewn case at 200–400 g empty can undercut a comparable blow-molded case at 800–1,500 g by 50–70%, and this delta is the dominant reason wearables suppliers list custom soft sewn alongside rigid options [S1].
Tooling cost drives off-the-shelf vs custom: vacuum forming uses low-cost aluminum molds (USD 1,500–6,000 typical band), while injection-molded tooling for plastic cases commonly starts at USD 15,000–60,000 per part, which forces the MOQ conversation to the front of the supplier RFQ [S1].
Comparison: Five Shell Types Against Four Buyer Criteria
For medical-device OEM buyers, hybrid 300 and hybrid 500 series cases combine a rigid blow-molded or injection-molded outer shell with a custom-EVA foam insert, sitting in the mid-band of the matrix where drop survival and cosmetic finish both matter [S1].
Who Each Construction Family Is For — And Who Should Skip It
Pick custom EVA when the payload is light (under 2 kg), the shock duty is severe, the run is under 500 units, and a soft-touch interior is required to protect coated optics or painted housings — this is the format medical diagnostic kit suppliers default to [S1].
Pick vacuum forming when cosmetic finish, branding embossing, and moderate IP are all on the spec, and when the budget cannot absorb injection-mold tooling; skip it for any application requiring verified drop survival above 1.2 m on hard concrete [S1].
Pick blow-molded cases for heavy tool kits, industrial measuring instruments, and field-service gear where a hollow double-wall geometry adds rigidity without proportional mass gain; skip it for sub-1 kg handhelds where the empty-shell mass is a penalty [S1].
Pick plastic-injected for volumes above 1,000 units where repeatability of hinges, latches, and gasket grooves is critical, and where IP67+ is required; skip it for prototypes and clinical-trial quantities because the amortized mold cost per part becomes punitive below ~500 pieces [S1].
Pick soft sewn for sales-demo kits, wearables, and lightweight instrument belts where flexibility and pack-flat storage matter more than impact survival; do not specify it for any payload where drop survival above 0.8 m is contractual [S1].
Standards, Compliance, and Sourcing Triggers
Buyers in regulated industries — medical devices, industrial measuring instruments, and electronics — typically need case suppliers to document material compliance (REACH, RoHS, FDA-grade foams where skin contact occurs) and to support lot-traceable production; current custom-case OEM sites list medical, electronics, optics, hardware & measuring, and industrial among their published vertical coverage [S1].
Drop testing commonly follows procedures modeled on ASTM-style repetitive-drop protocols at 1.0–1.5 m onto concrete or steel, while IP ratings on injection-molded and blow-molded shells are quoted against IEC 60529 dust and water ingress bands; buyers should request the supplier's test report and revision date before RFQ closure [S1].
Lead time behaves predictably across the five process families: EVA and soft sewn cases can be prototyped in 7–14 days, vacuum-formed in 14–21 days, blow-molded in 21–35 days once tooling is released, and injection-molded in 6–10 weeks including mold build — these bands are consistent with the production cycles published by current custom-case manufacturers [S1].
Real Use Cases From Industrial Carrying-Case Portfolios
Medical-device carrying cases: diagnostic handhelds and home-care instruments are typically specified in custom EVA shells with medical-grade inner foams and biocompatibility documentation, the dominant format offered by suppliers serving medical OEMs for two decades or more [S1].
Industrial measuring and hardware kits: calipers, gauges, laser distance meters, and hand-held analyzers default to hybrid 300 / hybrid 500 cases (rigid outer, custom-EVA insert) because both impact survival and instrument retention under vibration are non-negotiable in field conditions [S1].
Optics, electronics, and sales-demo kits: optics modules and presentation cases lean toward vacuum-formed or soft sewn shells, balancing cosmetic finish against portability; for related spec-bound equipment decisions, see the plastics and resin application map for resin property reference and the baler machine spec guide for adjacent industrial-packaging duty cycles.
Limits, Failure Modes, and Engineering Trade-Offs
EVA cases fail at seam peel under repeated flexure if the bonded joint is undersized for the payload — request peel-strength data in N/mm and accelerated-aging reports rather than relying on catalog claims [S1].
Vacuum-formed cases show wall-thickness variation (±15% is common) and visible draw-down at deep recesses, which can compromise both cosmetic finish and impact uniformity; specify a minimum wall-thickness tolerance in the RFQ [S1].
Blow-molded cases can warp near gate locations and across wide temperature swings, so HDPE/PP grade selection and seasonal shipping environment must be agreed in the supplier audit; plastic-injected cases avoid this failure mode but introduce sink marks at thick ribs unless the mold-flow analysis is requested up front [S1].
Soft sewn cases fail at stitch rows under sustained load, and welded TPU seams can crack below −20 °C unless the polymer grade is qualified for the deployment temperature band [S1].
Shortlist Logic for the Next RFQ
Map the payload mass and drop requirement to one of the five process families using the spec bands above, then lock the IP target and minimum order quantity before approaching suppliers — these three numbers eliminate roughly 70% of the catalog noise and let buyers compare like-for-like quotes from EVA, vacuum, blow-mold, injection, and soft sewn vendors [S1].
For the relevant spec sheets and selection criteria, see case packing machine, pressure transmitter, and flow meter.