What is coverall:
http://en.wikipedia.org/wiki/Overall
coverall also call boilersuits, is a one-piece garment with full-length sleeves and legs like a jumpsuit, but usually less tight-fitting. Its main feature is that it has no gap between jacket and trousers or between lapels, and no loose jacket tails. It often has a long thin pocket down the outside of the right thigh to hold long tools. It usually has a front fastening extending the whole length of the front of the body up to the throat, with no lapels. It may be fastened with buttons, a zip, velcro, or snap fasteners. Boiler suits with an attached hood are available.

Work wear and uniforms using in the fields of steel industry, mining, petroleum, automotive, logistics, catering, construction, medical, education, etc. for the coverall material mainly use is cotton, polyester or function flame resistant fabric. all these material with different weight, the quality will better if the fabric weight is high. different type fabric have different feature.

Coverall made of pure cotton is more comfortable, thickness, density, durability and suitable to resist all kinds of weather.

Cotton fabrics for reference:
16*12, 108*56, 260g/m2-270 g/m2
10*10, 72*40, 280g/m2-270 g/m2
10*10, 80*46, 290g/m2-310 g/m2
20*16, 120*60, 235g/m2-245 g/m2
21*21, 108*58, 190g/m2-200 g/m2
20*20, 108*56, 180g/m2-190 g/m2
21/2*10, 728*40, 270g/m2-280 g/m2
7+7*7+7,68*38, 380 g/m2
7+7*10/2,84*30, 400 g/m2
7+7*6,78*28, 340 g/m2

Fabric information for reference:
1. http://info.fabrics.net/fabric-facts/cotton/
Its production is one of the major factors in world prosperity and economic stability. Cotton “breathes”. What would we do without cotton? Since cotton wrinkles, polyester was added to give it wash and wear properties for a busy world. In recent times, the consumer determined that polyester, although easier to care for, took away the cool from cotton and also added a “pilling” effect to cotton/polyester blends. Consumers now often request “100% Cotton”. Permanent finishes also added to the all cotton fabric gave a wash and wear property to cotton. The cotton fiber is from the cotton plant’s seed pod The fiber is hollow in the center and, under a microscope looks like a twisted ribbon. “Absorbent” cotton will retain 24-27 times its own weight in water and is stronger when wet than dry. This fiber absorbs and releases perspiration quickly, thus allowing the fabric to “breathe”. Cotton can stand high temperatures and takes dyes easily. Chlorine bleach can be used to restore white garments to a clear white but this bleach may yellow chemically finished cottons or remove color in dyed cottons. Boiling and sterilizing temperatures can also be used on cotton without disintegration. Cotton can also be ironed at relatively high temperatures, stands up to abrasion and wears well. for different cotton type can check this link.

2. http://en.wikipedia.org/wiki/Cotton
Cotton is used to make a number of textile products. These include terrycloth for highly absorbent bath towels and robes; denim for blue jeans; cambric, popularly used in the manufacture of blue work shirts (from which we get the term “blue-collar”); and corduroy, seersucker, and cotton twill. Socks, underwear, and most T-shirts are made from cotton. Bed sheets often are made from cotton. Cotton also is used to make yarn used in crochet and knitting. Fabric also can be made from recycled or recovered cotton that otherwise would be thrown away during the spinning, weaving, or cutting process. While many fabrics are made completely of cotton, some materials blend cotton with other fibers, including rayon and synthetic fibers such as polyester. It can either be used in knitted or woven fabrics, as it can be blended with elastine to make a stretchier thread for knitted fabrics, and apparel such as stretch jeans.

Workwear made of P/C is more comfortable, thickness, breathable,durability and wrinkless

A blend of cotton polyester gives the durability at the same time giving cotton comfort to the user. Cotton polyester fabrics are basically in 2 categories:

1. CVC (Chief Value Cotton) – In this warp is full polyester in 80 or 150 Deniers and WEFT is 100% cotton in 40’s or 50’s. The resultant blend can be maintained 50/50.
2. We also use intimate blended polyester cotton yarn in counts of 100/2 and 80/2. The advantage of this fabric as it is made from spun yarn the comfort level is more with easy maintenance.

Workwear made of pure polyester is feeling fullness, elasticity, lines clear and soft gloss.
http://en.wikipedia.org/wiki/Polyester
for some cheap price work wear use polyester as material. Polyesters include naturally-occurring chemicals and synthetics. Natural polyesters and a few synthetic ones are biodegradable, but most synthetic polyesters are not. Polyesters may change shape after the application of heat and are combustible at high temperatures. They tend to shrink away from flames and self-extinguish upon ignition. Polyester fibers have high tenacity and E-modulus as well as low water absorption and minimal shrinkage in comparison with other industrial fibers.