D. be covered with a rugged, smooth cloth. (multiple layers of cloth and seams are permitted if needed to accommodate R27, provided the cross section in Figure 4-7 is not significantly altered).
Silk or bedding are not considered rugged materials, however 1000D Cordura is. Tape (e.g. gaffer’s tape) matching the BUMPER color is allowed to patch small holes on a temporary basis.
This wording of this rule is intentionally wide to permit cloth available in different parts of the US and internationally. The 1000D Cordura is my cloth of choice and the basis for comparison of other fabric. Inspectors have seen teams try to use a variety of fabrics over the years. Many held up in battle and many did not. In general, if you can see through it, if it is intended for clothing or it available in flowered patterns as well as solid colors it is likely not to survive this game. The smooth refers to fabrics that have woven in features like corduroy, etc. I believe the intent is to prevent you robot from getting caught (by the bumper fabric) on field pieces, borders and other robots.
If your fabric is the type used in laptop cases, back packs and luggage, it is likely to survive inspection and the game.