DRAFT ZANZIBAR NATIONAL STANDARD  
 
 
Envelop e — Specification  
 
 
 
 
 
 
 
 
 
 
 
ZANZIBAR BUREAU OF STANDARDS  
   
   ©ZBS 202 2 - All rights reserved                                                          First Edition  
 
  
                                                                                                  PCD 429: 2022  
                                                   ICS 35.260.20                                                                                
 
                            PCD 429: 2022  
©ZBS 2022 - All rights reserved  ii 
 Foreword   
This draft Zanzibar National standard has been developed by Stationary and paper product Standards 
Technical Committee (TCC5). In accordance with ZBS general procedures, this draft standard is presented to 
the public in order to receive any technical and e ditorial comment concerns.  
 
The Zanzibar Bureau of Standard (ZBS) was established under Standard Act No. 1 of 2011.  
 
In the preparation of this Draft Zanzibar National  Standard assistance was drawn from the following 
documents:  
IS 13892:2016  Correspondence envelopes – Specification  
IS 1060, (Part 3): 2019 Methods of sampling and test for paper and allied products  
 
Technical Committee Representatives  
 
This draft Zanzibar National Standard was prepared by Stationary and paper product Standards Technical 
Committee which consists of representatives from the following organizations:  
 
Chief Government Chemist Laboratory Agency (CGCLA)  
Department of Environment (DoE)  
Zanzibar Government Printing Press agency (ZAGPA)  
Zanzibar Library Services Board (Z LSB)  
Supplier Yaks  
Department of Forest (DoF)  
Zanzibar Bureau of Standards (ZBS) – Secretariat  
 
 
 
 
 
Zanzibar Bureau of Standard (ZBS)  
P.O.Box 1136  
Zanzibar  
Tel:  +255 24 2232225  
Fax: +255 24 2232225  
E-mail: info@zbs.go.tz  
Web:www.zbs.go.tz     
 
 
 
 
 PCD 429: 2022  
  
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Envelop e - Specification     
 
1 Scope  
 
This Draft Zanzibar National  Standard prescribes  the designations, requirements and methods of sampling 
and test for  correspondence envelopes in general and machineable  mail in particular intended to be sent by 
post.  
2  Normative references  
 
For the purpose of this Draft Zanzibar  Nationa l Standard, the following references shall apply:  
ZNS 94, Rounding off numerical values.  
PCD 431 , (Part 1) Methods of sampling and test for paper and allied products  
 
ISO 216:2007, Writing paper and certain classes of printed matter — Trimmed sizes — A and B series, and 
indication of machine direction  
 
ISO 478:1974, Paper — Untrimmed stock sizes for the ISO -A Series — ISO primary range  
 
ISO 593:1974 , Paper — Untrimmed stock sizes for the ISO -A Series — ISO supplementary range  
 
IS 2257, Paper adhesives, liquid gum and office paste type  
ISO 269 , Correspondence envelopes — Designation and sizes  
ISO 535 , Paper and board — Determination of water absorptiveness — Cobb method  
ISO 536 , Paper and board — Determination of grammage  
ISO 2494, P aper and board — Recommended procedure for the determination of roughness — Constant -
pressure air -flow method  
PCD 430 , Method for determination of porosity of paper  
 
ISO 1831, Printing specifications for optical character recognition   
 
ISO 24253 , Random sampling and randomization procedures  
 
 
3 Terms and definitions  
 
For the purpose of this  draft Zanzibar National standard the following (terms and) definitions shall apply:  
 
3.1  
Banker Shape  
With opening on the longer side of the envelope.  
 
 
 PCD 429: 2022  
©ZBS 2022 - All rights reserved  2 
 3.2  
Bottom Flap  
The flap on the bot tom of the pocket type envelope gummed to the body  to seal the bottom, saving the contents 
from falling out.  
 
3.3  
Machineable Mail  
First class letters and card s satisfying the requirements of dimensions and paper parameters which make them  
amenable for processing in high speed automatic mail processing machines.  
 
3.4  
Pocket Shape  
With opening on the shorter side of the envelope.  
3.5  
Print Contrast  
The difference between the reflectance of a character and that of the paper on which it is printed.  
 
3.6  
Print Contrast Signal (PCS)  
The ratio, Print contrast divided by the reflectance of the paper on which the character is printed. Also  
known as print contrast ratio. 
 
3.7  
Sealing Flap  
The flap on the top edge of the envelope which will act as a closure. This flap may or may not be gummed.  
 
3.8  
Seam  
The central point running parallel to the height of the pocket type envelope. It may be in the centre or the 
side.  
 
3.9  
Window  
A rectangular cut -out made in the face of an envelope and filled with a transparent material through which an 
address or other information shall be read.  
 
4 Types  
The envelopes shall be of the following two types depending on their shape, namely:  
 
a) Type 1 — Pocket shape envelope, and  
b) Type 2 — Banker shape envelope.  
 
Both these types may be with or without window.  
 
NOTE — Pocket shape should be discontinued gradually as it causes rejection in automatic mail sorting 
machine.  
 
Correspondence envelopes shall be designated by a reference to the type followed by an indication of size.  
 
 
 PCD 429: 2022  
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Table 1 : Dimensions of Envelopes  
S/NO  Size symbols  Size (mm)  
i.  - 90 x 140  
ii.  - 90 x 152  
iii.  - 100 x 176  
iv.  - 105 x 230  
v.  DL1 110 × 220  
vi.  C6 114 × 162  
vii.  B6 122 × 176  
viii.  C5 162 × 229  
ix.  B5 176 × 250  
x.  C4 229 × 324  
xi.  B4 250 × 353  
xii.  C3 324 × 458  
xiii.  9 X 4  101 X 228  
xiv.  A5 148 X 210  
xv.  A4 210 X 297  
xvi.  A3 297 X 420  
xvii.  X-RAY 420 X 490  
 
NOTE : Other dimensions shall be as agreed to between purchaser/supplier and manufacturers . 
1) Dimension lengthwise.  
 
5 Materials  
 
5.1  Paper  
 
The grammage of the paper used shall be dependent on the area of the envelope and it shall be as per  
Table 2, when tested by the method prescribed in ISO 536 . 
 
 
Table 2: Grammage of paper  
 
Area of envelop  (× 103 mm2) Grammage (g/m2 ) min 
Up to 30  70 
31 to 80  90 
81 to 120  120 
121 and above  140 
 
5.1.1  Surface of the paper shall normally be with uniform structure; free from dust/dart, blemishes, creases, 
specks, holes, etc. Mineral filling shall not cause corrosive or abrasive damage to transport means.  
 
5.1.2  Colour  of the paper shall be white or  coloured.  
 
5.1.3  The paper shall be dimensionally stable and flat when kept in ambient conditions of 20 -80 percent  
relative humidity and 15 to 35°C temperature.  
 
5.1.4  The paper shall also comply with the requirements given in Table 3.  PCD 429: 2022  
©ZBS 2022 - All rights reserved  4 
 5.2 Cloth Lining  
 
The cloth lining shall be of cotton, grey unbleached and/or plain wove. The cloth, when visually examined, 
shall be reasonably free from all defects, such as knots, joints, holes, cuts, weaving defects, etc.  
 
5.2.1  Ends and picks of the lining cloth per centimeter  shall be 9 to 10 and the substance shall be 45 ± 2 g/m2. 
 
 
5.3 Window Material  
 
The glassine paper of 35 g/m2, cellophane paper of 40 g/m2 or PVC/BOPP of 15 micron thickness shall  
be used as window material. The material shall stick firmly without any wrinkles to the inner side of plain front 
of the envelope.  
 
5.3.1  Transparency shall be adequate to ensure proper legibility to text under the window with normal sight.  
Print contrast signal (Print contrast ratio) of address  with respect to the background shall be at least 40  percent 
when tested according to ISO 1831.  
 
 
6 Requirements   
 
6.1 General  
The envelope shall be a flat case, generally rectangular in shape and made from one sheet of paper.  
 
6.1.1  The paper shall be so folded as to provide a plain front and a back consisting of four overlapping flaps. 
Three flaps shall be stuck together and completely sealed while the fourth, which may or may not be gummed, 
serves as a closure (or sealing flap) ( see Fig. 1). The left and right side flaps shall be sealed  under the bottom 
flap. 
 
6.1.1.1  In case the fourth flap is gummed, the adhesive used for this purpose shall be re -moistenable, non -
hygroscopic, non -toxic and of vegetable or synthetic type. The adhesives used for  making the envelopes shall 
be of good quality  and may not deteriorate with age or under particular environmental condition.  
 
6.1.2  The paper used for making envelope may be cloth lined, if desired by the purchaser.  
 
6.1.3  The front or working side may have a window f itted with transparent material ( see 5.3). 
 
6.1.4  The overlay between envelope and envelope window shall be glued carefully and completely to the inner 
side of the envelope and shall be located outside the reserved area for bar coding.  
 
6.1.5  The lowest part of the ad dress side of the envelope, 20 mm wide, covering the whole length of the 
envelope shall be reserved for bar coding.  
 
6.1.6  The inner portion of the envelope may be tinted, if desired by the purchaser; design and shade of tint  
shall be as agreed to between the purchaser and the supplier.  
 
6.2 Joints   
 
The pasting of the joints, wherever required, shall be  even and continuous without leaving any gap or  opening. 
The gum applied on the sealing flap, seam  and bottom flap shall not extend beyond the overlapping  portion. 
The left and right side flaps shall be  sealed under the bottom flap.  
 
6.2.1  The width of the bottom flap and the seam shall be between 1.5 cm and 2.5 cm to ensure the strength 
of the envelope and the safety of its contents.  PCD 429: 2022  
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6.3 Flaps  
 
The flaps for closing the enve lopes shall be of suitable shape, as agreed to between the purchaser and the 
supplier. Their width shall be such that it closes the envelope securely and ensures the safety of its content.  
 
NOTE: The adhesive applied on the sealing flap should not go beyond the overlapping area so that it 
should not stick to the letter in the envelope.  
 
 
 
Table 3: Requirements for Paper for Correspondence Envelopes  
S/NO  Characteristics  Requirements  Test methods  
i.  Burst index N m2/g, Min 2.0 PCD 431  (Part 1)  
ii.  Tear index (Machine  
direction), mN m2g,  
Min 12.0 PCD 431  (Part 1)  
iii.  One minute Cobb test:  
 
a) For both top and  
wire side, Max 
 
b) Difference between  
top and wire side  
Cobb value, percent,  
Max  
 
22 
 
 
15  
ISO 535  
iv.  Stiffness (Taber):  
 
a) 15° in direction of  
grain  
 
b) 15° across the grain   
 
 
2-20 
 
1-10  
 
Annex A  
v.  Smoothness (Bendtsen),  
ml/min (for both top and  
wire side)    
50-300  
ISO 2494  
vi.  Porosity (Gurley),  
100 ml/s, Min  10 PCD 430  
vii.  Opacity, Min 85 PCD 431  (Part 1)  
 
 
6.4 Size 
 
6.4.1   Dimensions of Envelopes  
The nominal dimensions of envelopes shall be as given in Table 1.  
6.4.2  Dimensions of Windows  
For envelopes with window, the nominal dimensions of the window shall be 39 mm × 93 mm, distance of the 
left edge of window from left edge of envelope shall be 20 mm and di stance of lower edge of window from 
bottom of envelope shall be 20 mm.  PCD 429: 2022  
©ZBS 2022 - All rights reserved  6 
 6.4.3  Tolerances  
The tolerance on all nominal dimensions given in Table 1 shall be ±2 mm.  
6.5 Printing  
The envelopes, if required, may be suitably and distinctly printed as agreed to between the purchaser and the 
supplier. This printing shall be on the smooth surface of the paper and at least 2.0 cm away from any of the 
edges. Six boxes for Pin number of sizes as given in postal envelope, if required, shall be printed above 20 
mm from the bottom e dge at the right -hand side leaving 20 mm from the edge. One box of sizes 30 mm × 30 
mm or 40 mm × 25 mm for stamp shall be printed at the top right -hand corner leaving 20 mm from both the 
sides.  
7 PACKING AND MARKING  
7.1 Packing  
The correspondence envelopes shall be securely packed as agreed to between the purchaser and the 
supplier.  
7.2 Marking  
Each package shall be marked with the following information:  
a) Indication of the source of manufacture,  
b) Size of the envelope,  
c) Number of envelopes in the package, and  
d) Batch number with month and year of manufacture.  
 
 
7.2.1  The product may also be marked with the Standard Mark.  
 
7.2.2  The use of the Standard Mark is governed by the provisions of Bureau of Zanzibar  Standards  and the 
Rules and Regulations made thereunder. The details of conditions under which the licence for the use of 
Standard Mark may be granted to manufacturers or producers may be obtained from Zanzibar  Bureau of 
Standards.  
 
 
8 Samp ling 
 
The number of correspo ndence envelopes to be  sampled (n) from each lot shall be as given in Table 4.  
 
 
 
Table 4 : Scale of Sampling  
Lot Size ( N) 
(Number of Envelopes)  Sample Size  
(n) Acceptance No.  
Up to 100  5 0 
101 to 150  8 0 
151 to 300  13 1 
301 to 500  20 1 PCD 429: 2022  
7                                                                                                                   ©ZBS 2022 - All rights reserved  501 to 1 000  32 2 
1 001 to 3 000  50 3 
3 001 to 10 000  80 5 
10 001 and above  125 7 
 
  
 
8.5 Criteria for Conformity  
 
a) While conducting the tests for paper quality,  no failure shall occur for the lot to be accepted  as conforming 
to this specification.  
 
b) An envelope shall be termed as defective if it  fails in one or more visual or dimensional  requirements (as 
per 5.1.1 to 5.1.4 , 5.2, 5.3, 6.1 to 6.5). The number of defectives in the  sample  shall be less than or equal to 
the permissible number of defectives [acceptance  number as per Table 4, col 3] for the lot  to be accepted as 
conforming to this  specification.  
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 PCD 429: 2022  
©ZBS 2022 - All rights reserved  8 
 Annex A  
Normative  
Test for stiffness  
 
 
A.1 Apparatus:  
The apparatus shall consist of the following:  
a) sample holder in which the test piece can be clamped;  
b) Means of applying a controlled bending moment to be portion of the test piece protruding from the 
clamp, the moment arm being 10 mm in length; and  
c) Suitable scales to indicate simultaneously the angular deflection of the moment··arm and the bending 
moment applied.   
A .2 Test Pieces - Representative test pieces 15 mm wide and about  50 mm long shall be cut from the sample 
in both the machine and the  cross directions.  
A .3 Procedure  
A .3.1 Clamp a test piece in the holder so that the free end of  the piece  projects 15 lo 20 mm. Apply the 
bending load at such a rate that the  moment arm is deflected through 5° in 5 seconds. Note the value of the  
bending moment and releas e the load. Repeat the operation three or four  times. Record the average bending  
moment for the test piece in g.cm  for a 5° deflection in 5 seconds, neglecting the first reading.  
A.3.2 Cut the next piece in the same direction but deflect it in the  opposite sense that is towards or away from 
the front side as the case may  be. Test at least four test pieces in each sense from the machine direction  and 
an equal number from the cross direction.  
A .3.3 Calculate the bending moment in the machine and the cross  directions separately and report the 
average as the stiffness of the sample.  
A .3 The value may also be expressed as stiffness factor as follows:  
 
Stiffness factor = average stiffness  
10 t3  
   
 
where;  
 
          t = thickness in mm