Here is some information about High Tensile Bags
Common materials used for 'High Tensile'(HT) bags:
Low density polythene (LDPE)
Linear low density polythene (LLDPE)
Medium density polythene (MDPE)
Recycled polythene
Available Thickness:
80 Gauge(20microns) to 250 Gauge(62.5microns)

Tolerances:
Normally, 'High Tensile(HT) bags' in Great Britain should follow widely accepted industrial standards according to British Standard - see BS7344, 1990 Width: Plus or minus 3mm (0.125") or 2% whichever is greater
Length: Plus or minus 6mm (0.25") or 2% whichever is greater
Gauge: Plus or minus 10%
Standards for 'High Tensile(HT) bags' to use for food contact and medical application:
Food Contact – To use High Tensile(HT) bags inside European Union, in contact with food should comply with the relevant legislation on food contact including Great Britain.
Great Britain: Statutory Instrument, 1998 No. 1376 and BPF-BIBRA (1995), Polymer Specification 4, Polyethylene
EU: Commission Directive 90/128/EEC, 92/39/EEC, 93/9/EEC, 95/3/EEC and 96/11/EC, Section A.
Example of a company comply with food contact: Polybags Limited
Medical use – Similarly, to use High Tensile(HT) bags inside European Union, to produce containers for preparations for medico-pharmaceutical purposes should comply with the following regulation:
European Pharmacopoeia - Monograph 3.1.3 "Polyolefin's" for medico-pharmaceutical purposes.
The final responsibility for the decision of whether a material is fit for a particular application lies with the pharmaceutical firm.
Example of a company comply with medical use: Polybags Limited