How does one make sense of the myriad of backpackable sleeping bags on today's market? How can a buyer get good value and long life from his carefully-made purchase and yet know that he will sleep comfortably this spring?

Let's begin by defining what we want. Summer lightweight bags don't contain enough down or synthetic insulation (synfills) to keep sleepers warm from April through June unless they're camping in the Tropics. Winter- weight bags with warmth ratings down to 0 degrees and below are overkill. And "spring" is a misnomer. What we really want is a three-season sleeping bag--spring, cool summer nights and fall--and that means a bag that will protect to 20 degrees.

But will it, protect to 20 degrees, that is? No standard exists across the industry: a 20-degree-rated bag from North Face is not a 20-degree-rated bag from Coleman. Why? Because too many variables, over which manufacturers have no control, must be considered. What a person eats or drinks before retiring to bed helps determine how warm (or cold) he will be. Alcohol, for example, lowers body temperature. Foods high in fat content stoke the body's furnace longer.

Whether or not you sleep with an inch-thick, closed-cell foam pad or atop the bare ground makes an enormous difference in how warm your sleeping bag is. Other factors include altitude, wind, exposure and how you dress for bed. On a 30- degree night in the Rocky Mountains in late May, one sleeper is toasty warm in his 20-degree-rated sleeping bag. Another shivers, while a third sweats.

So, a good night's sleep begins with the choice of the right bag, for you. To pick a winner, let's walk through the maze of insulation materials.

Down, especially goose or duck down, is the warmest material in the world. It is extremely light and lofts better than synfills. To get the best, buy "100-percent down"; otherwise, your bag could contain up to 20-percent poultry feathers. Fill-power refers to down's ability to loft. A bag with 700-fill is better (and more costly) than one with 550-fill.

Hollofil is DuPont Dacron insulation popular in entry- level bags because it is among the more affordable insulators. Hollofil II is made of four-hole, coated fibers designed to trap air for warmth. Hollofil 808 is made of single-hole hollow fibers warmer than solid-core polyester. Light in weight, the fibers also dry quickly.

Quallofil, also from DuPont, is a seven-hole, specially coated fiber designed to be soft, durable and quick drying. Along with the Hollofils, it has been around for years and is used in more sleeping bags than any other synfill.

Micro-loft is DuPont's newest entry into the synfill wars. Five times thinner than a human hair, the insulating fibers are designed to retain warmth when wet. At equal weight, Micro-loft is supposedly warmer than down.

Lite Loft is 3M Thinsulate's new synfill that uses heat, instead of resin, to bind two different sizes of fiber. The result is a lightweight insulation that lofts even when wet.

Primaloft is what Albany International calls "true synthethic down insulation". Designed for extreme wet weather, the synfill is designed to be light, warm and highly compressible. Primaloft PL2 is a newer and less-expensive clone.

Polarguard HV from Hoechst Celanese is a second- generation synfill that is made as a continuous filament. A little bulkier to pack, it tends to hold up longer than other fibers.

Most of the products in this article feature double- offset quilt construction to avoid cold pinch points between liners and batts of insulation. Special construction designs are so noted.

A word about outer and inner fabrics: Most sleeping bags contain an outer shell of ripstop or taffeta nylon. Liners may be the same material, cotton or cotton/polyester. More pricey bags tend to contain microfibers such as Super Microft, Pertex and Versatech. Tightly woven, they allow some moisture to escape and are water repellent.

No sleeping bag, by itself, is waterproof (unless you contain it in a bivy sack) but a new and expensive microporous membrane called DryLoft from W. L. Gore might as well be is not guaranteed waterproof. Like original Gore- Tex, which is replaces and is 40 percent more breatheable than that original membrane, DryLoft is usually laminated to an outer shell of polyester.

Besides personal appeal, color can be functional: Dark- colored sleeping bags tend to dry out faster than light- colored ones. We present our spring lineup of 20 degree sleeping bags as entry-level (under $100), mid-range ($100 to $200) and upper-end ($200 and above). Entry-level

Remington's Vancouver is a big, rectangular-cut sleeping bag measuring 39 x 80 inches and yet comes with a stuff sack for backpacking. Nearly half of its 8 lbs. 12 ozs. of weight, however, is Hollofil 808 insulation. The outer fabric is taffeta nylon, and the liner is cotton flannel. Neat features: A zipper lock prevents accidental opening at night; an outside zippered chest pocket holds a watch and pocket change. Retail: $89.95. Contact Nelson/Weather- Rite, 14760 Santa Fe Trail Dr., Lenexa, KS 66215 (913-492- 3200).

Lafuma of France makes a wide range of sleeping bags containing down and various synfill insulations. The 4.2 lbs. Safari contains Aerofibre 4, a silicone-treated hollow fiber with many holes to trap air and continue to loft and provide warmth when wet. Outer colors are cedar and prune, the shell is a seamless nylon, and the liner is Softwill 50D. Neat feature: The Safari is a generous 90 1/2 inches long. Retail: $99. Contact: Lafuma America, 7034 Sophia Ave., Van Nuys, CA 91406 (818-780-7868). Mid-range

The Synergy 20 degree bag from Cascade Designs contains 2 lbs. of Polarguard HV inside a polyester shell of rustic red with teal. Overall weight is 3 lbs. 3 ozs. in the regular model. Neat feature: The Synergy comes with a Therm-a-Rest camping mattress attached in a sleeve beneath the torso section, providing warmth and comfort without restricting leg movement. Retail: $109. Contact: Cascade Designs, Inc., 4000 First Avenue South, Seattle, WA 98134 (800-531-9531).

Coleman has redesigned its Peak 1 mummy-style sleeping bags into three lines offering a wide range of choice. The model 8577-424 is one of seven bags in the Tier I class, all of which are 32 x 85 inches. The Quallofil bag features a three-inch draft tube, and insulated zipper gusset and guard. Retail: $119. Contact: The Coleman Co., Box 2931, Wichita, KS 67201 (316-261-3276).

The Arctic II modified mummy-cut bag from vauDe has a Lite Loft fill weight of 2 lbs. and checks in at 3 lbs. 5 ozs. overall. Length is 87 inches (a 93-inch long model is also available), and color is ultramarine outer and gray inner. Both fabrics are nylon. Neat feature: vauDe uses a European zone system of Extreme, Optimum and Comfort for rating its sleeping bags. The Arctic II model is 10 degrees optimum with -15 degrees extreme and 60 degrees comfort. Retail: $135. Contact: Northern Lights, Inc., Box 3413, Mammoth Lakes, CA 93546 (619-924-3833).

The Ultra Light from Wiggly's Inc. is the only bag in our lineup to contain Lamilite, an early continuous filament fiberfill from Hoechst Celanese. The core ingredient, Comfort Fil 7, is also used to make Polarguard. The black and royal Ultra Light weighs 3 lbs., 4 ozs. and comes in modified mummy design. Neat Feature: Each bag contains a pillow. Retail: $146. Contact: Wiggly's, Inc., Box 2124, Grand Junction, CO 81502 (303-241-6465).

Bean's 20 degree Lite Loft sleeping bag comes in both mummy (82 x 31) and rectangular (75 x 32) models. The cobalt outer/teal liner bags are also available in regular and long sizes (88 and 80 inches respectively). The regular mummy contains 1 lb. 7 ozs. of fill and weighs 3 lbs. Special features: Shingled-layer construction and snag-proof double- taped zippers with full draft collars. Retail: $135 to $150. Contact: L.L. Bean, Freeport, ME 04033 (207-865- 4761).

The Men's Lite N' Up 20 degree Lite Loft bag by Sierra Designs weighs 3 lbs. 1 oz. in regular model and 3 ozs. more in the long model. The mummy-style bag has a royal blue shell and a purple/charcoal liner of Silkstone Polyester Taffeta. Fat draft tubes and shoulder collars keep warm air in the bag. Neat feature: In addition to Sierra Design's lifetime warranty, Lite Loft synfill manufacturer 3M offers a Sleep Warm warranty program. Anyone dissatisfied with the warmth of their bag can call a toll-free number and trade up to a higher-rated Sierra Designs model. Retail: $150. Contact: Sierra Designs, 1255 Powell St., Emeryville, CA 94608 (800-423-6363).

The Arapahoe bag from Jack Wolfskin comes in regular or large size and left- or right-hand zipper. Synfill is Thinsulate Lite Loft, and overall weight is 2 lbs. 5 ozs. Color is petrol, red and Caribbean. Neat feature: The Pertex 4 tightly woven nylon lining is designed to breathe yet stop wind, is water repellent and soft to the touch. Retail: $159.99. Contact: Jack Wolfskin, Div. of JWA, Box 2487, Binghamton, NY 13902 (800-847-1460).

Marmot's Mistral, which comes in short, regular and long models and is designed for cold, wet weather, is the company's best seller. The shell and lining are made from 1.9 oz. Synsilk taffeta, and the shell is treated with HT Teflon Durable Water Repellent finish. Color of the mummy style bag is purple. Neat Feature: Synfills include both Primaloft and Thinsulate Lite Loft. Retail: $185. Contact: Marmot Mountain Ltd., 2321 Circadian Way, Santa Rosa, CA 95407 (707-544-4590).

Slumberjack's 32 x 84 inch Conquest holds 24 ozs. of Lite Loft synfill. The outer fabric and liner is mini- ripstop nylon in navy color with purple trim. Carry weight is 2 lbs. 14 ozs. Neat Feature: the Conquest's "Hot Hood" is lined with Thermastat and contoured to snub tight with draw cord and barrel lock. Retail: $190. Contact: Slumberjack, Box 7048-A, St. Louis, MO 63177 (800-233-6283).

The Early Frost from Caribou Mountaineering is a mummy- style bag with 1 lbs. 13 ozs. of Primaloft PL2 in a Louverloft construction. The bag features a trapezoidal foot section and draft tube with double zippers that open right or left. Nylon shell color is cobalt with pomegranate trim; liner of Antron is silver in color. Neat Feature: The Early Frost stuffs into a small package--only 8 x 16 1/2 inches. Retail: $190. Contact: Caribou Mountaineering, Box 3696, Chico, CA 95927 (800-824-4153).

The Husky 1000 is made in Austria by Gold-Eck. The company designs its mummy bags to have a narrow underside so that the double-layered GLT synfill wraps better around the sleeper. Neat Feature: The addition of a light, soft, breathable scrim called Thermoflect prevents condensation while increasing heat retention by 11 percent. Colors are turquoise outer and anthracite inner, and the shell and lining are ripstop nylon. Retail: $190. Contact: Gold-Eck of Austria, 6313 Seaview Ave., N.W., Seattle, WA 98107 (206- 781-0886).

REI Fat Cat +20 degree sleeping bag contains 550-fill goose down (1 lb. 14 ozs.) for a 5-inch loft and features a rectangular, extra-roomy design that is 80 inches long. Locking drawcords and 13-inch zippers at the shoulder permit adjustment for ventilation or to create a mummy-style hood if temperatures dive. The bright-blue shell and black lining are both nylon. Neat feature: the bag zips together with another Fat Cat model. Weight: 3 lbs. 11 ozs. Retail: $200. Contact: REI, 1700 45th Street East, Sumner, WA 98390 (800-426-4840). Upper-end

Moonstone's P.C.T. bag is packed with 700-fill goose down, yet weighs only 2 lbs. 8 ozs. in regular size. Variable thickness layering is wrapped to ground level to ensure that insulation goes above the sleeper. Neat features: More warmth can be added later by buying an Advanced Concept Liner in down, Lite Loft or Polarguard HV. Also, Gore Dryloft is a purchasing option. Retail: $299 ($375 with Dryloft). Contact: Moonstone Mountaineering, Inc. 5350 Ericson Way, Arcata, CA 95521 (707-822-2985).

The mummy-style VersaLite bag by Western Mountaineering contains 700-fill power goose down with 6-inch loft and yet weighs only 2 lbs., 3 ozs. Neat feature: An oversized draft tube and passive top collar (no draw cord or Velco fastener) lock cold out. Blue color shell is 1.1 oz. ripstop nylon, and inner construction is continuous baffles at 5 1/4 inch spacing with a red liner. Retail: $300. Contact: Western Mountain Sports, 1025 South 5th St., San Jose, CA 95112 (408- 287-8944).

Stephenson Warmlite Triple bags are designed to be comfortable from 60 degrees above zero to 70 degrees below. Each down-filled bag comes with a thin top for temperatures down to 25 degrees and a thick top for weather to minus 10 degrees. Putting the two tops together creates even more warmth. Neat Features: Each Warmlite Triple bag contains a vapor barrier liner to keep the down dry as well as a down- filled air mat. Retail: $399 to $810 depending upon size and model. Contact: Stephensons, 22 Hook Rd., Gilford, NH 03246 (603-293-8526). Unknown

The Cascade by MZH comes with an outer shell of AeroTec in green/gold color and triple-layer Micro-loft insulation. Neat feature: three sizes are available--28 x 78, 30 x 84 and 32 x 90. Synfill weights range from 1 1/2 to 2 lbs.; overall weight is 3 1/2 to 4 lbs. The bag's cobra mummy style hugs the body thanks to extra-wide gussetted shoulders and thinned-down legs. The sculpted hood features an extra face-protection baffle. Retail: $260 to $265. Contact: MZH, Inc. 80 East Route 4, Paramus, NJ 07652 (201-909-0777).

The Cat's Meow from The North Face is available in three tapered-mummy style sizes, all of which contain Polarguard HV. The small model holds 1 lb. 14 ozs. of insulation, weighs 3 lbs., and is 74 x 27. Color of the Super Microfiber shell is royal. Neat Feature: ThermaStat lining is soft as flannel and wicks away body moisture. Retail: Unknown. Contact: The North Face, Inc., 999 Harrison St., Berkeley, CA 94710 (510-527-9700).

The Olympic #49500 from Wenzel is a 33 x 84 inch mummy- style bag that contains 48 ozs. of Hollofil 808. The ripstop nylon shell is navy color with red trim; the nylon taffeta liner is royal blue. Retail: Unknown. Contact: Wenzel, 1224 Fern Ridge Parkway, St. Louis, MO 673141 (800-325-4121).

The Clear Creek 20 degree by Kelty comes in six models that provide options of size, fill weight and left and right-hand zippers. The standard, 30 x 72 incher contains 28 ozs. of Hollofil II and checks in at 3 lbs. 2 ozs. total weight. The outer shell of 50 denier nylon taffeta is blue- green in color and the poly/cotton liner is silver. Neat feature: Full-cut mummy design adds space; hood with drawstring prevents escape of warm air. Retail: Unknown. Contact: Kelty, Inc., New Haven, MO 63068 (800-423-2320).