NR in sheet forms are the oldest and the most popular type. Being the simplest and easiest to produce on a small sacle, small holder's rubber in most of the countries are processed and marketed as sheet rubber. Two types of sheet Rubbers are produced and marketed in the international market, namely the Ribbed smoked sheets (RSS) and the Air Dried Sheets (ADS). Among these two types, Ribbed smoked sheet is the most popular and is available for volume consumption.

RIBBED SMOKED SHEETS (RSS)

Ribbed smoked sheets are marketed based on visual assessment of quality. To establish acceptable grades for commercial purposes, the international Rubber Quality and Packing conference, have stipulated the grade description and the details are given in the Green Book.

THE INTERNATIONAL GRADE DESCRIPTIONS FOR RSS

Only deliberately coagulated rubber latex processed into rubber sheets, properly dried and smoked can be used in making RSS. The following prohibitions are also applicable to the RSS grade.
 
  Wet, bleached, undercured and virgin rubber and rubber that is not completely visually dry at the time of buyer's inspection is not acceptable(except slightly undercured rubber as specified for RSS-No: 5)
  Skim rubber made of skim latex shall not be used in whole or in part in the patches as required under packing specifications.
 
Prior to grading RSS, the sheets are separated, inspected and any blemishes are removed by cutting with a pair of scissors.

GRADE DESCRIPTIONS
No: IX RSS

The grade must be produced under conditions where all processes are carefully and uniformally controlled. Each bale must be packed free of mould but very slight traces of dry mould on wrappers or bale surfaces adjacent to wrapper found at time of delivery will not be objected to provided there is no penetration of mould inside the bale. Oxidised spots or streaks, weak, heated, undercured, oversmoked, opaque and burnt sheets are not permissible.

The rubber must be dry, clean, strong, sound and evenly smoked and free from blemishes, specks, rust, blisters, send, dirty packing and any other foreign matter. Small pinhead bubbles if scatteres, will not be objected to.

RSS No. 1

Each bale must be packed free of mould but very slight traces of dry mould on wrappers or bale surfaces adjacent to wrapper found at the time of delivery will not be objected to provided there is no penetration of mould inside the bale. Oxidised spots or streaks, weak, heated, undercured, oversmoked, opaque and burnt sheets are not permissible.

The rubber must be dry, clean, strong sound and from blemishes, rust, blisters, sand, dirty packing and any other foreign matter, except slight specks. Small pinhead bubbles, if scattered, will not be objected to.

RSS No. 2

Slight rust, and slight amount of dry mould on wrappers, bale surfaces and interior sheets, found at time of delivery will not be objected to, provided these conditions either singly or in combination, do not exist to an objectionable extent on and in more than 5% of the number of bales included in the delivery, lot or tender as determined by the number of bales inspected.

Small bubbles and slight specks of barks, if catteres, will not be objected to.

Oxidised spots or streaks, weak, heated, undercured, oversmoked, opaque and burnt are not permissible. The rubber must be dry, clean, strong, sound and free from blemishes, blisters, sand, dirty packing and all other foreign matter other than specified above as permissible.

RSS No. 3

Rust and dry mould on wrappers, bale surfaces and interior sheets, found at time of delivery will not be objected to, provided these conditions, either singly or in combination, do not exist to an objectionable extent on and in more than 10% of the number of bales included in the delivery, lot or tender as determined by the number of bales inspected. Slight blemishes in clour, small bubbles ans small specks of bark permissible. Oxidised spots or streaks, weak, heated, undercured, oversmoked, opaque and burnt sheets are not permissible. The rubber must be dry, strong and free of blemishes, blisters, sand dirty packing and all other foreign matter other than specified above as permissible.

RSS No. 4

Rust, dry mould on wrappers, bale surfaces and interior sheets, found at time delivery will not be objected to provided these conditions, either singly or in combination, do not exist to an objectionable extent on or in more than 20% of the number of bales included in the delivry, lot or tender as deteremined by the number of bales inspected.

Medium size bark particles, bubbles, translucent stains, slightly sticky and slightly over smoked rubber as permissible but should not be evident to a marked degree. Oxidised spots, or streaks, weak, heated, undercured opaque and burnt sheets are not permissible. The rubber must be dry, firm and free of blemishes, blisters, sand, dirty packing and all other foreign matter other than specified above as permissible.

RSS No. 5

Rust, dry mould on wrappers, bale surfaces and interior sheets, found at time of delivery will not be objected to provided these conditions, either singly or in combination, do not exist to an objectionable extent on or in more than 30% of the number of bales included in the delivery, lot or tender as determined by the number of bales inspected.