It seems like every major brand of sleep sacks has their own washing, and care instructions. While you can find brand-specific instructions on the manufacturers’ websites (see homepage for links to major brands), proper laundering should really be based on the type of fabric that the sleep sack is made out of.
Both Woolino and Merino Kids use Merino wool in the construction of their sleep sacks. Merino wool has a big advantage over other fabrics in that it naturally resists odor and some may even say it’s even self-cleaning to a point. The best way to take care of these premium sleep sacks is to turn them inside out often and air it out. When you do need to wash, either hand wash or machine wash on a delicate or “wool” cycle on low temperature. Be sure to fully close the zipper prior to washing and use a wool-approved laundry detergent (a minimal amount). Dry cleaning is also a good option. Because Merino wool dries so quickly, you can skip the dryer and simply drape over a drying rack or lay flat. If you must use the dryer, use a No Heat or Low Heat setting.
Aden + Anais uses this soft, breathable fabric in their sleeps sacks and while the material may seem delicate, it can be washed fairly similar to normal cotton. You may wash by hand or use the Normal or Gentle/Delicate cycle on your washing machine. Use either cold or warm water (warm for whites). Use a gentle laundry detergent (ie: Woolite) and be sure to remove the sleep sack from the washing machine as soon as the washing machine cycle is done to reduce the amount of wrinkles. It’s recommended to hang dry or flat dry and skip the drying machine.
The majority of sleep sack brands use good ‘ol cotton. Care and laundering is similar to clothes that are 100% cotton. Prior to washing, be sure to fasten any velcro closures. Optimally, the sleep sack will be closed up and turned inside out. Machine wash with like colors using color or warm water. Regular chlorine bleach may be used with cotton products if needed. You may hang-dry or machine-dry on a low temperature.
Laundering micro-fleece is almost identical to cotton. The biggest difference is that if you need to use bleach, you need to use a peroxide (color safe) bleach.