Waterproof clothing is simply clothing which keeps you dry in the rain. It keeps the wet on the outside leaving you dry and comfortable on the inside. It may sound pretty straightforward but there are so many types of waterproof fabric and degrees of waterproofness that careful consideration needs to be taken when purchasing such garments.
Waterproof fabrics are fabrics which have been treated to become resistant to penetration by water and wetting. For example, they may have been proofed with a spray substance which then affects the waterproofness.
If cost is an issue, or you are not sure how much use you will get from your new waterproof clothing, it is better to buy for the worst conditions you are expecting to wear the clothing in. If you are hiking up Snowdon for example, you will need to spend extra cash on a more technical garment in order to remain protected from the elements.
Nylon is a very lightweight choice for a waterproof as the clothing can be regarded as 'packable' and great for carrying. The fabric is strong and can be coated to provide a totally waterproof finish. Nylon can also be made into a ripstop fabric by using thicker threads through the weave. This gives the fabric extra strength. Nylon doesn't absorb much water and so takes very much less time to dry out than cotton. It is also quite cheap to produce compared to membrane fabrics, although not as effective as a waterproof.
The problem for manufacturers with nylon fabrics is that they deteriorate when exposed to sunlight, and are weakened when coated with the various waterproofing treatments. Nowadays there are also many breathable coatings which can be applied directly to the inside of a fabric. Better makes of jackets etc. have an inner lining layer to protect the coating and make the jacket more comfortable.
'Condensation control' or 'directional' fabrics are a more popular choice for longer periods of wear or more energetic activities due to their wicking nature. Such fabrics will keep you dryer as the water vapour is directed away from the body as well as keeping the rain on the outside. As they are also breathable fabrics, they ensure comfort during most outdoor sports.
Laboratory tests are carried out to determine the performance of any waterproof clothing fabric. The water resistance measurement is determined by suspending water over the fabric and allowing it to seep through. The British Standard is only 3 PSI, which is approx 1,500mm of pressure. Rain fall is approximately 2 PSI, so you will need a waterproof which is higher than the British Standard to keep you properly protected.
The Hydrostatic head test is the standard laboratory test performed on waterproof fabrics. This test pumps water though a cylinder which is placed over the fabric until the pressure is great enough to allow the water through.
Goretex is the original breathable membrane, made of microporous PTFE (polytetrafluoroethylene) plastic which will not let cold rainwater droplets in but allows warm water vapour to pass out through the tiny pores. It can be laminated to a variety of fabrics, or can also be sewn in as a separate lining between a non-waterproof outer and inner. There are several imitators of Goretex. Microporous membranes need to be kept clean, because the pores can clog up and prevent the water vapour passing through - leading to condensation.
One thing to check on waterproof clothing is the seams. Even a good strong seam will still leave little holes through which the thread passes and through which water can enter. On a good quality product these should be sealed. This is usually done with an appropriately coated tape covering the seam inside the garment. Fully waterproof PU coated or neoprene tape for the non-breathable fabrics and breathable tape to match the breathables. The seams of the garment are sealed to stop rain seeping through the waterproof fabric and into the garment through the stitched areas.
The ultimate decision is yours. Just remember that the more expensive items are going to provide better performance long term. Ask lots of questions when you buy to and hopefully you will get lots of wear from your waterproofs in the years to come!