Although fabric technologies have come a long way, there is a general rule, that the more waterproof a fabric is, the less breathable it is. This is especially true for cycling specific garments, where an athlete generates so much heat and sweat, that the only way for a cyclist to stay dry inside and out, is to have a garment that is not only made from a waterproof, breathable fabric; but through design and garment constrution, breathes and wicks moisture. For cycling specific garments breathability and moisture management are obtained through venting. You will have to look at the garment construction (vents) to get the optimum waterproof, breathability in a cycling specific rain garment.

The only manufacturer making a vented rain pant is a company called Showers Pass. For most other brands, breathability is limited to what the fabric technology can offer you given the outside temperature, and your level of exertion and sweat production. For warm weather cycling, your best option is not to wear pants at all. Wear a cycling rain cape and cycling specific sandals and enjoy the cooling effect of the rain.
More Info on Rain Capes

Companies That Make Cycling Specific Rain Capes

Campor Waterproof Rain Cape
(Suggested Retail $ 29.99)
Fabric: 8.5 oz coated taffeta nylon
Features:
Well designed hood for optimum visibility plus rain protection
Elastic thumb and leg loops keep the cape in place
2 in. x 6 in. reflective strip on the back
Stuff sack included
Colors: Yellow
Size: One Size Fits All

J&G’s Park Ranger Waterproof Rain Cape
(Suggested Retail $ 39.99)
Fabric: Nylon Oxford Cloth with a 1.5 polyurethane coating
Features:
Generously sized for maximum coverage.
Four-piece design and construction minimizes seams.
Waist tie
Hand grabs to keep it in place.
High collar has a drawstring and cord lock to adjust to your neck.
Reflective 3M-brand strip on the back with a hang tab for a blinking light.
Colors: Yellow
Size: One Size Fits All

Human Powered Machines Ultrex® Poncho
(Suggested Retail $ 49.99)
Fabric: Ultrex®
Features:
Colors: Yellow/Black, Blue/Black
Size: S- L

Carradice Duxback Rain Cape
(Suggested Retail $ 98.00)
Fabric: Polyester with a water resistant coating.
Features:
Adjustable side flaps for close, non flap fit
Mesh underarm vents
Detachable hood, Rear zipped pocket
Dropped hem at back
Comfortable lined collar and hood
Full length two way zip with storm flap
Long sleeves with adjustable cuffs
Jacket, over trousers and poncho all pack away into small drawstring pouch
Available in standard and super sizes
High elasticated waist to prevent draughts
Close cut legs to prevent flapping and chain snagging
Internal tapes secure to bike and cyclist
Zipped front opening makes for easy fitting over helmet
Calf length zips with storm flaps allow easy fitting
Leather pull tabs
Colors: Black
Size: One Size Fits All

Companies That Make Cycling Specific Sandals

Nashbar: Ragster Cycling Sandal
(Suggested Retail $64.99)
SPD compatible sandal. Synthetic leather upper, lined with neoprene. Three Velcro strap closure.
Sizes: 39/40,41/42,43/44,45/46

Exustar: E-SS220 Cycling Sandals
(Suggested Retail $69.99)
Upper: PU-coated natural leather, breathable mesh.
Sole: EVA / rubber
Fastener: Paiho Velcro over-strap
Footbed: Synthetic microfiber leather
Midsole: Bio Sole
Compatibility: SPD
Sizes: 39–40, 41–42, 43–44, 45–46
Weight: 776 g/pr
Recommended: Pedals E-PM85 Cleats E-C05

Lake: Style LXSDL
(Suggested Retail $79.99)
SPD compatible sandal. TeKtile™ synthetic leather upper with a molded heel provides. Two Velcro® fasteners.
Sizes: 37/38, 39/40, 41/42, 43/44, 45/46, 47/48

Shimano: Style SH-SD65
(Suggested Retail $79.99)
SPD compatible sandal. Synthetic leather and mesh upper. Rubber and EVA insole with padded heel support. The three Velcro® fasteners.
Sizes: 37/38, 39/40, 41/42, 43/44, 45/46, 47/48

Vittoria Free Cycling Sandal
(Suggested Retail $79.99)
SPD compatible sandal. Synthetic suede and honeycomb mesh upper with a neoprene tongue pad that conforms to the top of the foot providing an extremely comfortable fit. Two Velcro® straps.
The rubberized outsole with nylon insert.
Sizes: 39-48

Nike: Havasu Cycling Sandal
(Suggested Retail $84.99)
2 hole cleat compatible. Synthetic leather and mesh uppers. Nylon 6,6 insole plate provides stiff yet walkable support. Proprietary Nike BRS 1000 rubber outsole. Contoured and co-molded PU midsole/insole.
Sizes: 41 - 46

For cooler weather, you will want a cycling specific pant.
Features to look for:
All truly waterproof garments will have sealed seams.
Longer rear crotch inseam designed to accommodate the cyclist in the bent over cycling position.
Articulated knees for easier pedaling.
Leg openings that have zips or velcro so that you can get your pants on easily over cycling shoes.
Venting to increase breathability and temperature regulation.
Reflective trim for greater visibility.
Reinforced Seat.

The following are some options you can consider based on your specific needs and budget- pants retail from $ 21.95 to $ 199.95 depending on fabric and features.

Companies That Make Cycling Specific Rain Pants

O2 Yellow Rain Pant
(Suggested Retail $21.95)
O2 Rainwear Microporous Film is a very inexpensive, yet high-performance laminate. The company claims to have the best combination of water holdout and breathability of any fabric on the market today. Their Microporous Film is thin and lightweight, making O2 Rainwear™ easy to pack. The garment is known for its affordability- priced at the same price as non-breathable, rubber, plastic, and PVC-coated garments.
Features:
Gathered waist.
Packs into a compact stuff sack that fits inside a jersey pocket

3 Flow Performance Series Pants by Rain Shield
(Suggested Retail $68.99)
Constructed of Seam Sealed, Waterproof, Breathable, Windproof 3Flow™ Performance Fabric
Features:
Articulated knee panels,
Elasticized cuffs and waist,
Ankle zippers,
Back pocket

Fox Wear Power Shield Pants
(Suggested Retail $ 77.00)
Features:
Articulated knee allows for easy bending of the knee even with many layers.
Elastic at waist. No snaps.
Rugged, snag proof fabric
Warm and wind proof
Non Cling fabric
Reinforced Seat
Stretchable and breathable

Gill Freedom Pant
(Suggested Retail ?)
On-the-bike fit
100% waterproof & windproof
DWR silicon water repellent finish which beads the water off the face of the fabric
Fully taped seams
Breathable & durable
Articulated ‘pre-bent’ legs to mimic the natural riding position
High backed semi-elasticated waist with adjustable drawcord for a snug fit
28cm zip ankle closures with velcro protective flaps to make it easier to put on and take off
Lower leg reflective for increased visibility

Showers Pass Rain Pants (Suggested Retail $ 79.00)
Medium-weight waterproof, breathable fabric.
Cut for wear over other clothing - whether tights or commuter clothes.
Highest quality 3M reflective tape for night-time riding.
Elastic back and velcro waist closures (allows wide range of adjustment).
Ankle zippers so you can put on without removing shoes.
Double velcro ankle closure prevents chainring snags.
Fully taped seams to keep the rain out.
Size medium weighs about 12 ounces (340g).
The pants easily roll up for carrying in a jersey pocket or pannier. Size medium rolls to approximately 8" x 3.5" (20cm x 9cm).
Vents are in two places: the knee, and at the upper waist. We have constructed an articulated knee, sort of like a shingle, that uses a sturdy lycra panel to provide lower leg ventilation when pedaling. The vertical side pockets (with zipper closure) have a mesh liner, providing ventilation when the pockets are open. These four vents (two knees, two pockets) effectively prevent sweat buildup during hard efforts, like doing a long climb.

Endura Gridlock Pant
(Suggested Retail $ 79.00)
This versatile rain pant has taped seams and extended length ankle zips.
Durable inner ankle panels and ankle gusset.
djustable belt and zip fly.
Reflective taping near the ankle for increased visibility.

J & G Waterproof Breathable Rain Pants
(Suggested Retail $79.95)
These Waterproof Breathable Rain Pants are extremely durable and are made to last. They will last twice as long as other similar rain pants on the market, and at half the price. They are generously sized like our regular waterproof rain pants with the advantage of breathability and the addition of rear pockets and bottom leg zips. The rain pants have 3M-brand reflective tape, which has a far greater range and angle of reflectivity than other reflective tapes, at the ankles.
2-ply Nylon Supplex bonded to a waterproof breathable membrane allows body moisture to pass from the body through the pants; very supple, durable, and machine washable (hang dry)
Fully lined with nylon mesh to protect the waterproof membrane, and for comfort against the skin
Generously sized with full seat and high waist
Wide elastic waistband has an adjustable waist tie for maximum fit and comfort
Rear zippered pockets, two
Side zippered pocket access on both sides
Zippers at cuff for ease of slipping on and off over footwear
3M-brand reflective Velcro adjustments on cuffs for maximum fit and visibility
Color: Black
Sizes: SM - 3X

Pearl Izumi Arroyo Pant
(Suggested Retail $ 89.00)
Constructed from WxB fabric with taped seams that offers wind and waterproof protection, while remaining highly breathable.
Plush elastic waistband with drawstring.
Reflective dot design and logo increase low-light visibility for added safety.
Sizes: M (32-34), L (35-37), XL (38-41)

Foxwear Rain Pant
(Suggested Retail $ 95.00)
Features:
Now made of Power Shield with 2 weights to choose from
Cuffs can be made adjustable enough to go over the boot top (keeps rain out of the boot)
Draw string waist. No zippers. No snaps.
Secure Pockets (nice for cell phones)
Pockets located away from hips where you bend while riding
Rugged, snag proof fabric
Warm and wind proof
Non Cling fabric
Reinforced Seat
Mildly stretchable and breathable

Novara Stratos Rain Pants
(Suggested Retail $ 99.00)
A waterproof, windproof, breathable cycling pant made from a three-layer, polyurethane laminated nylon.
Features include:
Anatomical cut (higher rear inseam allows the pant to fit correctly when the cyclist is bent over the bike)
Articulated seat and knees.
Stretch panels at knees and gusset. Draw cord waist.
Reinforced right inner ankle protects against chain abrasion.
Ankle zippers for easy on/off over bike shoes.
Gripper elastic cuffs with hook-and-loop closures seal out water.
Reflective piping increases visibility in low-light conditions.
Small zip back pocket is sized to stash a few small items such as ID and some cash.

Burley Ultimate Commuter Rain Pant
(Suggested Retail $109.95)
Waterproof, windproof and breathable Gelanots fabric
70 denier fabric for long lasting durability
Fully seam taped and sealed
Articulated knees for superior comfort and fit
Full length 3M reflective piping
Leg zippers
Ankle and below-knee cinches
Side zippers and velcro-like closure that allow the pants to easily go on and off hips and also provides access to pockets on undergarments (see image below)
Machine washable - hang dry
Women’s specific sizing available

Pearl Izumi Instinct Waterproof Cycling Pant
(Suggested Retail $ 119.00)
W x B bombproof, windproof, waterproof, breathabe
Stretch inset knees
Fully taped seams keep water out
Articulated knees and gusseted crotch ensure a comfortable ride
Multi-snap waist and drawstring make pants easily adjustable
Rear pockets provide convenient storage
Off-set 8-inch ankle zippers with locking zipper tabs
Ankle pull tabs allow full protection
Very packable
Women’s specific sizing available.

Craft Bike Rain Pant
(Suggested Retail $ 129.00)
Lightweight Vent Air fabric is windproof, waterproof and breathable
Articulated knees
Reinforced crotch
Reflective piping
Fully lined with mesh fabric to prevent the pants from sticking to your skin
Ankle zip with snap button at bottom hem
2 adjustable straps on each pant leg
Zippered pocket at yoke back
Removable suspenders (see image at right)
Women’s specific sizing available.

GORE Bike Wear Ultra II Pant (Suggested Retail $159.99)
2-layer Gore-Tex Paclite laminate provides breathable, wind and Water protection
Stuff this pant into its own pocket or stow it in your jersey pocket for easy transport
Wear-resistant seat reinforcement, pre-shaped knees and adjustable leg width adds durable mobility
Elastic waist with drawcord ensures a perfect fit
Easy-off zippered ankles with reflective detailing keep you visible in overcast conditions

Gore-Tex®Paclite® Alpine Pants (Suggested Retail $ 199.99)
Shell: wind and waterproof Gore-Tex® Paclite® laminate fabric - highly breathable and packable Packs into its own back pocket with double zipper pulls
Cut specifically for women with a lower stretch front panel, comfortable elasticized waistband and high-cut back
Wear resistant reinforcement at seat and back of leg
Pre-shaped knee
Adjustable leg width with two velcro positions on leg closures for chain protection
Back zippered stow pocket doubles as its own stuff sack
Reflective piping on leg for safety
Reflective logos on calf and upper thigh