The choice should come from testing, not habit. The FTC Care Labeling Rule, 16 CFR Part 423, requires that a washing instruction say whether to hand or machine wash and give a water temperature unless hot water up to 145°F will not harm the product. The importer or manufacturer must also have a reasonable basis for the instruction, which can be reliable test evidence.

Why viscose needs care

Viscose is a regenerated cellulose fibre. In general, fabrics made from it are weaker when wet than cotton and can shrink or lose shape more easily if washed and dried too hard. That does not mean hand wash is the only option, because yarn, knit, finish and construction all differ. It means you should test washing, drying and shrinkage on the finished pajama set.

A test plan

Wash samples with a named procedure such as ISO 6330, using the programme you want to allow, for example a gentle machine cycle at a stated temperature, and compare with hand washing. Measure length and width before and after, and check for pilling, distortion, seam puckering and colour change. Check drying options: tumble low, line dry or flat dry. Repeat for several cycles.

Wording the label

If a gentle machine wash passes, use it, together with the drying instruction that passed. ISO 3758 symbols show milder cycles with bars under the washtub, according to GINETEX. If only hand wash passes, say hand wash and give the temperature. Warn against any usual step that would harm the garment, such as hot drying, in clear words. Make sure words and symbols agree.

Check the fibre name

Bamboo-based viscose is a rayon fibre, and FTC guidance on bamboo claims explains that such products should be labelled as rayon, and may say rayon made from bamboo if that is true. Do not call it bamboo fibre on the label.

Wording for EU sales

If you sell these pajamas into the EU, avoid vague environmental words such as “eco-friendly”, “green” or “sustainable” on the hang tag or product page. Directive (EU) 2024/825 applies from 27 September 2026 and prohibits generic environmental claims unless recognised excellent environmental performance can be demonstrated. A claim is not generic when its specification is given in clear and prominent terms on the same medium, and the Directive’s recitals say terms like “sustainable” should not rest on environmental performance alone. EU countries apply the Directive through national laws that can differ, so check each market.

Keep the evidence

Keep wash results with photos and measurements by style and update them when the fabric or finish changes. If customers will wash pajamas often, test more cycles than for a dressier item, and put the same instruction on the label, the product page and the packaging insert, so that a customer reading any one of them gets the same advice and the label stays consistent with what you tested.