Sleepsacks are a popular type of bondage (BDSM) gear. Sleepsacks are primarily used to confine a person comfortably for an extended period of time.  Similar to a conventional sleeping bag, a person climbs into a sleepsack and is usually zipped into it up to their neck. Generally sleepsacks are very tight on the body, adding to the bondage aspect of the experience.
Sleepsacks are designed so the person is as immobile as possible. There is generally a pocket at the bottom that the wearer's feet go into. A durable zipper runs from below the knees up to the neck. Generally sleepsacks have collars at the top which buckle around the neck, further securing the person in it. Instead of a single pull zipper most sleepsacks have triple zippers which allow for an opening anywhere along the length of the zipper. Sleepsacks with the zipper as described will also usually have internal arm sleeves. With arms in the internal arm sleeves the wearer is unable to have access to any part of his or her body.
Sleepsacks can be made from several different types of materials. Each type of material offers a different experience. The most popular material is probably leather. Other types of sleepsacks are rubber, canvas, Darlex, and Neoprene.
Leather sleepsacks are generally very confining but do not stretch. If they are sized correctly they are very comfortable for long-term usage. Leather for the most part does not allow moisture to accumulate (i.e., sweat). Many bondage enthusiasts spend entire nights comfortably in leather sleepsacks. In order to make the tightest fit possible many leather sleepsacks have buckles which go around the body. Many also have lengths of rope which are laced along various points on the top of the sleepsack and cause it to tighten around the person's body.
Leather sleepsacks are the most durable type of sleepsack and often come with bondage hooks or rings for attaching further restraints. Leather sleepsacks can also be suspended upright with the appropriate knowledge and equipment. Many leather sleepsacks also come with separate zippers near the nipples and buttocks. Leather sleepsacks are also the most expensive, costing up to $1,000 or more.
Rubber sleepsacks are also very confining but do have some stretch. This natural stretch is what causes rubber sleepsacks to be confining and tight. As with leather the sizing of a rubber sleepsack is very important for a proper fit. People who have a rubber fetish interest like rubber sleepsacks for obvious reasons.
Rubber sleepsacks do not disperse moisture at all. For this reason hydration is a very important consideration for people who spend any amount of time in a rubber sleepsack. Sweating can often be profuse even if the occupant is only lying inside it. All fluids from the body accumulate in the sack, which also makes the rubber sleepsack a choice for those who are also have a urination fetish. Rubber sleepsacks are easy to clean as they can simply be rinsed with water. Sweat leaking out from the neck can often occur while lying flat and should be a consideration.
Darlex sleepsacks are made of a spandex-like material. Darlex stretches much like spandex but is much more durable. One main benefit of Darlex sleepsacks is they are significantly cheaper than leather and rubber, and can accommodate a wider range of sizes due to how much it can comfortably stretch. Although still very confining Darlex does not put as much compression on the body as rubber, making it more comfortable to stay in for longer periods of time.
Sleepsacks in BDSM culture Edit
Sleepsacks are an effective way to secure somebody comfortably, but also tightly, for long periods of time. Generally someone will need to be assisted into and out of a sleepsack by another person. There are neck-entry type sleepsacks which are open at the top and do not have a full zipper.  These types of sleepsacks are good for those who want to have a similar experience on their own.
The immobility that sleepsacks cause to the occupant is a major reason they are popular. Sleepsacks also provide a great way to secure someone for many types of bondage and BDSM play, which may or may not include sexual activity.
Safety considerations Edit
As with any type of bondage, there are considerations that must be taken prior to entry into sleepsack bondage.
- Never leave someone alone. Should any type of unforeseen circumstance arise (such as fire, police raid, etc) it will be impossible for the person in the sleepsack to get out.
- Hydration. As in any type of long-term bondage and especially in rubber, dehydration is a major and often underestimated problem.
- Watch that zipper. Since most people who want to be in a sleepsack also will want to be naked, making sure all body parts are away from the zipper is obvious but important enough to mention.
- Circulation issues. A general rule of bondage is the person being restrained should change positions about once every hour to prevent circulation problems. Sleepsacks are often an exception to this rule as the body is held in a position to allow for normal circulation. That said there are still opportunities for problems with extended time in a sleepsack. Often issues arise with the shoulder area being overly compressed or the arms not fitting properly into the sleeves. Preventing this from getting to be a real problem goes back to the #1 rule of not being left alone.
- Safeword. Also a general rule of bondage/BDSM play, having a safeword available for someone to use when they really need to be released is very important. 
- Power exchange. Giving up control of a situation to someone else.
- Tactile sensations. The tactile feeling of the material involved.
- Loss of control. The feeling of restraint and helplessness.
- Comfort. Comfortable for long-term bondage; many fantasies of waking up in bondage are satisfied by falling asleep then waking up in a sleepsack.
- Ease of use. Generally very easy to get into, does not require lots of equipment or knowledge of bondage techniques.
- Combining equipment. Can be easily combined with hoods creating a feeling of total or near total sensory deprivation.
- Other play. With the heavy-duty triple zipper on many sleepsacks it is easy to incorporate many elements of BDSM play, including CBT, orgasm control and orgasm denial.
- 'Sleep sack' Encyclopervia entry at Informed Consent
- Safeword chapter in soc.subculture.bondage-bdsm FAQ