Most RFQs that stall don’t stall on the hard questions. They stall on the material line — a callout that looks complete but doesn’t actually tell the shop what to buy or why. Here are the seven material spec mistakes that cross the quote desk most, each with its consequence and its one-line fix.
1. Specifying “plexiglass” as if it were a spec
Plexiglass is a genericized trademark for acrylic, not a material grade. Writing it on a drawing communicates “acrylic” and nothing else — not cast versus extruded, not thickness, not optical requirement. The fix: say acrylic, then add cast or extruded only when the application makes it matter. And if the quote names a sheet type, what the quote says we build with is what we build with.
2. Choosing polycarbonate “to be safe” for display work
Polycarbonate’s impact resistance is real, and irrelevant to a countertop display that nothing will ever hit. Choosing it anyway pays polycarbonate’s penalties — edges that never arrive where a polished acrylic edge does, more scratch-prone surfaces, outdoor yellowing in uncoated grades — for protection the shelf never needed. The fix: ask what the part must survive. If the answer is “being looked at,” acrylic is almost always the better display material.
3. Choosing acrylic for a machine guard
The reverse error. Where the panel’s job is absorbing impact — guards, high-abuse barriers, anything that gets hit — impact resistance rules the decision, and that is polycarbonate’s territory. Hearing that from an acrylic shop is the point — the recommendation follows the hazard, not the sale. The fix: same question, opposite answer: when the part exists to take a hit, spec the material that takes hits.
4. Specifying material but not thickness
“1 sheet acrylic, clear” is unquotable. Thickness drives weight, stiffness, cost, process selection, and whether the part works at all — leaving it off guarantees a clarification round-trip before the quote can even start. The fix: every material callout carries a thickness. If you don’t know the right one, say what the part holds or spans and let the shop propose it — that is a faster path than silence.
5. Ignoring UV exposure in the material call
An interior-grade material specified for an outdoor or sunlit installation fails slowly and in public — yellowing, embrittlement, a sign face that looks tired well before the program is done with it. Acrylic is naturally UV-stable, which is one reason sign faces are so often acrylic; other plastics need the exposure stated so the right grade gets sourced. The fix: one word on the RFQ — interior or exterior — and sun exposure if it’s unusual.
6. Specifying “clear plastic” on an optical part
Clear plastics are not interchangeable where optics matter. Light transmission, inherent tint, haze, and edge appearance all differ by polymer — acrylic’s clarity and water-white edge behavior are why it carries display work, while other clears carry a cast that compounds with thickness. On a part whose job is being seen through, “clear plastic” delegates the most important property to chance. The fix: name the optical requirement — true-clear at this thickness, polished edges, no visible tint — and the polymer choice follows.
7. Copying a metal or wood detail into plastic unchanged
Drawings inherited from metal or millwork carry details that crack plastic: fine tapped threads, sharp inside corners, zero-clearance press fits, fastener torque specs carried over unchanged. Acrylic in particular concentrates stress at sharp geometry and rewards radiused corners, oversized clearance holes, and hardware designed for it. The fix: when a detail was designed for another material, flag it for review rather than carrying it over — a one-line note that saves a cracked first article.
The pattern behind all seven
Every mistake on this list is the same mistake wearing different clothes: the spec names a material instead of a requirement. Name the requirement — impact, UV, optics, load, span, viewing distance per the Quality Standards — and the material call becomes checkable, by you and by the shop quoting it. The RFQs that quote fastest are the ones where the material line answers why, not just what. Send the requirement with the drawing, and the clarification round-trips disappear.
