This wader repair primer is about holes and tears, but not seam leaks. For seam leaks, send the waders to the manufacturer. The manufacturer is the best source of information for proper repairs and care. Their recommendations trump any found herein.
Breathables are king of the hill. Several top manufacturers no longer offer neoprene. Outside of Wayne's fishing shack, when was the last time anyone saw vulcanized rubber waders? The nylon/urethane lightweights have just about disappeared from the sellers shelves.
What lurks in your fishing closet is another thing entirely. On the premise that the hole represents less than one percent of the wader, doesn't it make sense to patch the hole to protect the good ninety-nine percent of your investment (and keep your wallet closed a little longer)? Whether your waders are made of neoprene and/or fabric (nylon or polyester) coated with PVC or urethane or bound to a layer of waterproof-breathable film, they are very repairable.
A number of adhesives will make a patch on all these materials. The author of a magazine article I recall from several years back tested a variety of adhesives. He found that those made specifically for wader patching performed better than what you'll find at a hardware store. You'll easily find these products:
To fix a pin-hole leak, you've got to find it. Don't fill your waders with water (Simms says to do it this way!) and look for wet spots on the outside. The pressure of the water could very likely burst seams. (I suspect that the seams of good breathables are much stronger than the butt-glue-tape seams of neoprenes.) A usually safe method that does use water puts the waders in the water, not the water in the waders. Gather the wader top around the nozzle of a blowing, not sucking, vacuum cleaner. Immerse and examine the waders a bit at a time. The idea is to gently inflate the waders which will cause air to bubble through any leaks. If the waders are weak from age or use or high heat or ozone damage or their bargain-basement geneology, they might not survive even gentle inflation. Ask Mike McGuire about his father-in-law's exploding waders. To avoid the stress of pressurizing your waders, use a strong flashlight pressed against the inside of the waders. In a darkened room, slide the flashlight around as you watch for pin-points of light. A fourth method uses a spray of alcoholdon't use Pinelli's gin. The alcohol will penetrate the pinhole and show as a dark spot on the opposite side. Whichever method you use, when a leak is found, X or circle it with a marking pen.
Dabbing the goo of your choice over the pinhole and, for neoprene, working it into the hole is probably all that's necessary. A fabric patch is overkill.
To fix a tear or large hole, you should use goo with a bit of fabric. Waders often come with a patch of material for repairs. Better than that is a bit of nylon stocking. You will get the best result if the repair goo sticks to the waders, impregnates the stocking patch, and makes a thin skin over all of it. (This is general good practice in fiberglassing, an essentially similar process.) Depending on the tack and curing time of the goo you use, this might be done in one step or several.
The cloth patch should be on the outside of the waders, unless you prefer the inside. (Research for this article turned up recommendations both ways, when mention of a preference was made at all.) Belt plus suspenders type individuals will, of course, patch outside and inside. Because of the folding, creasing, and stretching in the crotch, put a patch on both sides of leaks in this area. If you use a bit of nylon stocking, you'll find it wants to curl. It takes a bit of gentle poking to flatten it. You'll find the curled edges annoying when you use your waders, so take the time to make the patch flat. Goo with heavy viscosity or light tack helps with flattening the fabric. The patch must extend beyond the damage a bit. The manufacturer applied seam tape overlaps each side of a seam by five millimeters (a quarter-inch for you Americans). I'd not overlap less than that.
In contradiction to the opening admonition to send seam leaks back to the factory, I have had success on neoprene seams using hot-melt glue and sometimes just the hot nozzle of the hot-melt glue gun to re-melt the existing glue. The technique is light on glue and heavy on using the hot nozzle to thoroughly smooth the seam tape. If you can't wait weeks for the return of your waders, if they're out of warranty, or if you're an inveterate tinkerer, try this at your own risk.
When adhesive is applied to a hole or tear, there is the possibility that the adhesive will leak through. This might result in cementing the waders shut or to the workbench. Some tape applied to the side opposite to the one getting the adhesive will prevent bonus attachments. It also holds the repair area together as the patch is being applied and as it is curing. To be super-safe, slip some waxed paper inbetween the to-be-glued and the not-to-be-glued.
Breathablity will be suffocated in patch areas. You probably won't notice.
If your breathable waders seem clammier than they used to be, it's not lots of pinholes nor is the breathable film clogged. Failure of the exterior fabric's water repellency is almost always the cause. If water doesn't bead on the outer surface, your waders (and jacket, too) need attention. Start with washing, if water still doesn't bead, re-apply water-repellent. Your waders may have come with some instructions for resoring water repellency. Consult the Patagonia website for typical instructions. Customer Service < Product FAQs Patagonia recommends Nikwax (select outerware care); the author has found it to work well. Patagonia notes that there are "many good products on the market".
If your socks are always soggy, but you can't find a leak in your wader booties, the neoprene is probably broken down (cell walls torn). This is inevitable after a lot of wear. The booties take a lot of abrasion and compression. You can try to stop the damp by painting goo all over the bootie, but it probably won't restore them to their former dryness. Tom Kilfoil has touted the comfort of SealSkinz waterproof, breathable socks. They might give you an extra season or three in those oozing, yet fully paid for, old waders.
Your most desperate situation is a leak too big to live with while you're in the middle of great fishing. You need to get those waders fixed NOWno drying them, no waiting overnight for the goo to cure. The UV cure product from Loon Outdoors is what you want. It works on dry or wet waders, it cures in minutes, the tube is so small that you can carry it with you all the time. It has saved the day for the author and fishing companions. (You can buy a UV lightsize of a lipstickfrom Loon for when the sun don't shine.)
Get some of this right away. Put it in your vest. Have it with you onstream. Get a small square of pantyhose, tooyour wife ruins about four pair per week, and she has the nerve to complain about the expense of fly fishing. If you don't get this stuff now, some day you'll find yourself sitting on the bank watching through your tears as Phil Drees catches fish after fish after fish. And he won't even feel bad about it.
Behind curtain two is Orvis Wader Repair Tape. Some fly shops seem to still have it listed among their products, but the Orvis website doesn't list it. This tape fixes holes and tears in a few moments. You can then go fishing immediately. Expect to need to replace this patch after a few wearings.