14 CFR § 31.33 - Materials.

---
identifier: "/us/cfr/t14/s31.33"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "14 CFR § 31.33 - Materials."
title_number: 14
title_name: "Aeronautics and Space"
section_number: "31.33"
section_name: "Materials."
chapter_name: "FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION"
subchapter_number: "C"
subchapter_name: "AIRCRAFT"
part_number: "31"
part_name: "AIRWORTHINESS STANDARDS: MANNED FREE BALLOONS"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "49 U.S.C. 106(g), 40113, 44701-44702, 44704."
regulatory_source: "Docket No. 1437, 29 FR 8258, July 1, 1964, as amended by Amdt. 31-1, 29 FR 14563, Oct. 24, 1964, unless otherwise noted."
cfr_part: "31"
---


# 31.33 Materials.

(a) The suitability and durability of all materials must be established on the basis of experience or tests. Materials must conform to approved specifications that will ensure that they have the strength and other properties assumed in the design data.

(b) Material strength properties must be based on enough tests of material conforming to specifications so as to establish design values on a statistical basis.